February 25, 2017

Artist’s impression of the exoplanet seen from its moon

exoplanet from moon

The diversity of exoplanets is large — more than 3500 planets outside the Solar System have been found to date, with thousands more waiting to be confirmed. Detection methods in this field are steadily and quickly increasing — meaning that many more exoplanets will undoubtedly be discovered in the months and years to come.

Image Credit: IAU/L. Calçada

Supercell and Lightning over Kansas

Supercell and Lightning over Kansas

Leoti, Kansas, USA
May 21, 2016

Image Credit & Copyright: Max Conrad

Supernova Remnant SN 1987A

Supernova Remnant SN 1987A

Three decades ago, a massive stellar explosion sent shockwaves not only through space but also through the astronomical community. SN 1987A was the closest observed supernova to Earth since the invention of the telescope and has become by far the best studied of all time, revolutionising our understanding of the explosive death of massive stars.

Located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, Supernova 1987A is the nearest supernova explosion observed in hundreds of years. It marked the end of the life of a massive star and sent out a shockwave of ejected material and bright light into space. The light finally reached Earth on 23 February 1987 — like a cosmic blast from the past.

The NASA/ESA Hubble Space Telescope has been on the front line of observations of SN 1987A since 1990 and has taken a look at it many times over the past 27 years. To celebrate the 30th anniversary of the supernova and to check how its remnant has developed, Hubble took another image of the distant explosion in January 2017, adding to the existing collection.

Because of its early detection and relative proximity to Earth, SN 1987A has become the best studied supernova ever. Prior to SN 1987A, our knowledge of supernovae was simplistic and idealised. But by studying the evolution of SN 1987A from supernova to supernova remnant in superb detail, using telescopes in space and on the ground, astronomers have gained revolutionary insights into the deaths of massive stars.

Back in 1990, Hubble was the first to see the event in high resolution, clearly imaging the main ring that blazes around the exploded star. It also discovered the two fainter outer rings, which extend like mirror images in a hourglass-shaped structure. Even today, the origin of these structures is not yet fully understood.

However, by observing the expanding remnant material over the years, Hubble helped to show that the material within this structure was ejected 20 000 years before the actual explosion took place. Its shape at first surprised astronomers, who expected the dying star to eject material in a spherical shape — but faster stellar winds likely caused the slower material to pile up into ring-like structures.

The initial burst of light from the supernova illuminated the rings. They slowly faded over the first decade after the explosion, until the shock wave of the supernova slammed into the inner ring in 2001, heating the gas to searing temperatures and generating strong X-ray emission. Hubble’s observations of this process shed light on how supernovae can affect the dynamics and chemistry of their surrounding environment, and thus shape galactic evolution.

Image Credit: NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics)
Explanation from: https://www.spacetelescope.org/images/heic1704a/

February 24, 2017

Exoplanet TRAPPIST-1f

Exoplanet TRAPPIST-1f

TRAPPIST-1f (also known as 2MASS J23062928-0502285 f) is an exoplanet, likely rocky, orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1 40 light-years (12.1 parsecs) away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope.


Mass, radius, and temperature

TRAPPIST-1f is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 219 K (−54 °C; −65 °F). It has a radius of 1.04 R⊕. The mass has not yet been estimated, but based on its size, a mass of around 0.68 M⊕ is possible.


Host star

The planet orbits an (M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 M☉ and a radius of 0.11 R☉. It has a temperature of 2550 K and is at least 500 million years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerably less metal content than the Sun. Its luminosity (L☉) is 0.05% of that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.


Orbit

TRAPPIST-1f orbits its host star with an orbital period of about 9.206 days and an orbital radius of about 0.037 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).


Habitability

The exoplanet was announced to be either orbiting within or slightly outside of the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. TRAPPIST-1d has a radius of around 1.16 R⊕, so it is likely rocky. Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live. Because of this ability to live for long periods of time, it is likely TRAPPIST-1 will be one of the last remaining stars when the Universe is much older than it is now, when the gas needed to form new stars will be exhausted, and the remaining ones begin to die off.

The planet is very likely tidally locked, with one hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. However, between these two intense areas, there would be a sliver of habitability – called the terminator line, where the temperatures may be suitable (about 273 K (0 °C; 32 °F)) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

Image Credit: NASA/R. Hurt/T. Pyle
Explanation from: https://en.wikipedia.org/wiki/TRAPPIST-1f

Exoplanet TRAPPIST-1e

Exoplanet TRAPPIST-1e

TRAPPIST-1e (also known as 2MASS J23062928-0502285 e) is an exoplanet, likely rocky, orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years (12.1 parsecs) away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

It was one of seven new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope. The exoplanet is within the star's habitable zone.


Mass, radius, and temperature

TRAPPIST-1e is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 251.3 K (−22 °C; −7 °F), which is close to Earth's equilibrium temperature. It has a radius of around 0.92 R⊕ and a mass of 0.62 M⊕. It also has a similar density to Earth as well.


Host star

The planet orbits an (late M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 M☉ and a radius of 0.11 R☉. It has a temperature of 2550 K and is at least 500 million years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerably less metal content than the Sun. Its luminosity (L☉) is 0.05% of that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.


Orbit

TRAPPIST-1e orbits its host star with an orbital period of about 6 days and an orbital radius of about 0.028 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).


Habitability

The exoplanet was announced to be either orbiting within the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. TRAPPIST-1e has a radius of around 0.92 R⊕, so it is very likely rocky. Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live. Because of this ability to live for long periods of time, it is likely TRAPPIST-1 will be one of the last remaining stars when the Universe is much older than it is now, when the gas needed to form new stars will be exhausted, and the remaining ones begin to die off.

The planet is very likely tidally locked, with one side of its hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. However, between these two intense areas, there would be a sliver of habitability – called the terminator line, where the temperatures may be suitable (about 273 K (0 °C; 32 °F)) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

Image Credit: NASA/R. Hurt/T. Pyle
Explanation from: https://en.wikipedia.org/wiki/TRAPPIST-1e

Exoplanet TRAPPIST-1d

Exoplanet TRAPPIST-1d

TRAPPIST-1d (also known as 2MASS J23062928-0502285 d) is an exoplanet, likely rocky, orbiting within or slightly outside the habitable zone around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years (12.1 parsecs) away from Earth in the constellation of Aquarius. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.


Mass, radius, and temperature

TRAPPIST-1d is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 288 K (15 °C; 59 °F). It has a radius of 1.16 R⊕. The mass has not yet been estimated, but based on its size, a mass of around 1.7 M⊕ is possible.


Host star

The planet orbits an (M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 M☉ and a radius of 0.11 R☉. It has a temperature of 2550 K and is at least 500 million years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerly less metals then the Sun. Its luminosity (L☉) is 0.04% of that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.


Orbit

TRAPPIST-1d orbits its host star with an orbital period of about 4.05 days and an orbital radius of about 0.0214 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).


Habitability

The exoplanet was announced to be either orbiting within or slightly outside of the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. TRAPPIST-1d has a radius of around 1.16 R⊕, so it is likely rocky. Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live. Because of this ability to live for long periods of time, it is likely TRAPPIST-1 will be one of the last remaining stars when the Universe is much older than it is now, when the gas needed to form new stars will be exhausted, and the remaining ones begin to die off.

The planet is very likely tidally locked, with one hemisphere permanently facing towards TRAPPIST-1 and the other shrouded in darkness. However, between these two intense areas, there would be a sliver of habitability – called the terminator line, where the temperatures may be suitable (about 273 K (0 °C; 32 °F)) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

During formation of the system, it is possible that water loss during its first few million years of existence occurred. This was likely due to photoevaporation.

TRAPPIST-1d may have kept enough water to remain habitable depending on its initial content. The two innermost planets, b and c, probably lost up to four times the amount of Earth's oceans, depending on their composition.


Discovery

A team of astronomers headed by Michaël Gillon of the Institut d’Astrophysique et Géophysique at the University of Liège in Belgium used the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama desert, Chile, to observe TRAPPIST-1 and search for orbiting planets. By utilising transit photometry, they discovered three Earth-sized planets orbiting the dwarf star; the innermost two are tidally locked to their host star while the outermost appears to lie either within the system's habitable zone or just outside of it. The team made their observations from September to December 2015 and published its findings in the May 2016 issue of the journal Nature.

Image Credit: NASA/R. Hurt/T. Pyle
Explanation from: https://en.wikipedia.org/wiki/TRAPPIST-1d

Comparing the TRAPPIST-1 planets

Comparing the TRAPPIST-1 planets

A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres.

Image Credit: NASA/R. Hurt/T. Pyle

Comparison between the Sun and the ultracool dwarf star TRAPPIST-1

Comparison between the Sun and the ultracool dwarf star TRAPPIST-1

This image shows the Sun and the ultracool dwarf star TRAPPIST-1 to scale. The faint star has only 11% of the diameter of the Sun and is much redder in colour.

Image Credit: ESO

February 22, 2017

TRAPPIST-1 Planetary System: 3 Earth-Size, Habitable-Zone Planets Around Single Star

TRAPPIST-1 Planetary System: 3 Earth-Size, Habitable-Zone Planets Around Single Star

NASA's Spitzer Space Telescope has revealed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water – key to life as we know it – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”

At about 40 light-years (235 trillion miles) from Earth, the system of planets is relatively close to us, in the constellation Aquarius. Because they are located outside of our solar system, these planets are scientifically known as exoplanets.

This exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. In May 2016, researchers using TRAPPIST announced they had discovered three planets in the system. Assisted by several ground-based telescopes, including the European Southern Observatory's Very Large Telescope, Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

The new results were published Wednesday in the journal Nature, and announced at a news briefing at NASA Headquarters in Washington.

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them, allowing their density to be estimated.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated – scientists believe it could be an icy, "snowball-like" world, but further observations are needed.

"The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star," said Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium. "It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds."

In contrast to our sun, the TRAPPIST-1 star – classified as an ultra-cool dwarf – is so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun. The planets also are very close to each other. If a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of neighboring worlds, which would sometimes appear larger than the moon in Earth's sky.

The planets may also be tidally locked to their star, which means the same side of the planet is always facing the star, therefore each side is either perpetual day or night. This could mean they have weather patterns totally unlike those on Earth, such as strong winds blowing from the day side to the night side, and extreme temperature changes.

Spitzer, an infrared telescope that trails Earth as it orbits the sun, was well-suited for studying TRAPPIST-1 because the star glows brightest in infrared light, whose wavelengths are longer than the eye can see. In the fall of 2016, Spitzer observed TRAPPIST-1 nearly continuously for 500 hours. Spitzer is uniquely positioned in its orbit to observe enough crossing – transits – of the planets in front of the host star to reveal the complex architecture of the system. Engineers optimized Spitzer’s ability to observe transiting planets during Spitzer’s “warm mission,” which began after the spacecraft’s coolant ran out as planned after the first five years of operations.

"This is the most exciting result I have seen in the 14 years of Spitzer operations," said Sean Carey, manager of NASA's Spitzer Science Center at Caltech/IPAC in Pasadena, California. "Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets.”

Following up on the Spitzer discovery, NASA's Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone. These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets.

In May 2016, the Hubble team observed the two innermost planets, and found no evidence for such puffy atmospheres. This strengthened the case that the planets closest to the star are rocky in nature.

"The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets," said Nikole Lewis, co-leader of the Hubble study and astronomer at the Space Telescope Science Institute in Baltimore, Maryland. NASA's planet-hunting Kepler space telescope also is studying the TRAPPIST-1 system, making measurements of the star's minuscule changes in brightness due to transiting planets. Operating as the K2 mission, the spacecraft's observations will allow astronomers to refine the properties of the known planets, as well as search for additional planets in the system. The K2 observations conclude in early March and will be made available on the public archive.

Spitzer, Hubble, and Kepler will help astronomers plan for follow-up studies using NASA's upcoming James Webb Space Telescope, launching in 2018. With much greater sensitivity, Webb will be able to detect the chemical fingerprints of water, methane, oxygen, ozone, and other components of a planet's atmosphere. Webb also will analyze planets' temperatures and surface pressures – key factors in assessing their habitability.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around

TRAPPIST-1 Planetary System

TRAPPIST-1 Planetary System
This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultra cool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them.

This artist’s impression is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe.

Astronomers have found a system of seven Earth-sized planets just 40 light-years away. Using ground and space telescopes, including ESO’s Very Large Telescope, the planets were all detected as they passed in front of their parent star, the ultracool dwarf star known as TRAPPIST-1. According to the paper appearing today in the journal Nature, three of the planets lie in the habitable zone and could harbour oceans of water on their surfaces, increasing the possibility that the star system could play host to life. This system has both the largest number of Earth-sized planets yet found and the largest number of worlds that could support liquid water on their surfaces.

Astronomers using the TRAPPIST–South telescope at ESO’s La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.

Dips in the star’s light output caused by each of the seven planets passing in front of it — events known as transits — allowed the astronomers to infer information about their sizes, compositions and orbits. They found that at least the inner six planets are comparable in both size and temperature to the Earth.

Lead author Michaël Gillon of the STAR Institute at the University of Liège in Belgium is delighted by the findings: “This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!”

With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms — only marginally bigger than the planet Jupiter — and though nearby in the constellation Aquarius (The Water Carrier), it appears very dim. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life, but TRAPPIST-1 is the first such system to be found.

Co-author Amaury Triaud expands: “The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our Sun. Planets would need to be in far closer orbits than we see in the Solar System if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1!”

The team determined that all the planets in the system are similar in size to Earth and Venus in the Solar System, or slightly smaller. The density measurements suggest that at least the innermost six are probably rocky in composition.

The planetary orbits are not much larger than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1’s small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water — assuming no alternative heating processes are occurring. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water.

These new discoveries make the TRAPPIST-1 system a very important target for future study. The NASA/ESA Hubble Space Telescope is already being used to search for atmospheres around the planets and team member Emmanuël Jehin is excited about the future possibilities: “With the upcoming generation of telescopes, such as ESO’s European Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope, we will soon be able to search for water and perhaps even evidence of life on these worlds.”

Image Credit: ESO/M. Kornmesser
Explanation from: https://www.eso.org/public/news/eso1706/

Artist’s impression of the surface of the exoplanet TRAPPIST-1f

Artist’s impression of the surface of the exoplanet TRAPPIST-1f

This artist's concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius.

Because this planet is thought to be tidally locked to its star, meaning the same face of the planet is always pointed at the star, there would be a region called the terminator that perpetually divides day and night. If the night side is icy, the day side might give way to liquid water in the area where sufficient starlight hits the surface.

One of the unusual features of TRAPPIST-1 planets is how close they are to each other -- so close that other planets could be visible in the sky from the surface of each one. In this view, the planets in the sky correspond to TRAPPIST1e (top left crescent), d (middle crescent) and c (bright dot to the lower right of the crescents). TRAPPIST-1e would appear about the same size as the moon and TRAPPIST1-c is on the far side of the star. The star itself, an ultra-cool dwarf, would appear about three times larger than our own sun does in Earth's skies.

The TRAPPIST-1 system has been revealed through observations from NASA's Spitzer Space Telescope and the ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope, as well as other ground-based observatories. The system was named for the TRAPPIST telescope.

Image Credit: NASA/JPL-Caltech/T. Pyle (IPAC)
Explanation from: http://www.spitzer.caltech.edu/images/6274-ssc2017-01c-Surface-of-TRAPPIST-1f

Artist’s impression of view from planet in the TRAPPIST-1 planetary system

Artist’s impression of view from planet in the TRAPPIST-1 planetary system

This artist’s impression shows the view just above the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultracool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them.

This artist’s impression is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe.

Image Credit: ESO/N. Bartmann
Explanation from: https://www.eso.org/public/images/eso1706l/

Artist’s impression of view from distant planet in the TRAPPIST-1 planetary system

Artist’s impression of view from distant planet in the TRAPPIST-1 planetary system

This artist’s impression shows the view just above the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultracool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them.

This artist’s impression is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe.

Image Credit: ESO/N. Bartmann
Explanation from: https://www.eso.org/public/images/eso1706q/

Artist’s impression of view from one of the middle planets in the TRAPPIST-1 planetary system

Artist’s impression of view from one of the middle planets in the TRAPPIST-1 planetary system

This artist’s impression shows the view just above the surface of one of the middle planets in the TRAPPIST-1 system, with the glare of the host star illuminating the rocky surface. At least seven planets orbit this ultracool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them.

This artist’s impression is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe.

Image Credit: ESO/N. Bartmann
Explanation from: https://www.eso.org/public/images/eso1706r/

February 21, 2017

Earth and HTV-6 spacecraft seen from International Space Station

Earth and HTV-6 spacecraft seen from International Space Station

The Japanese HTV-6 cargo craft is pictured in the grips of the Canadarm2 after it was detached from the Harmony module of the International Space Station. Astronauts Thomas Pesquet of ESA (European Space Agency) and Commander Shane Kimbrough of NASA were at the controls of the robotic arm before commanding it to release the resupply ship.

ISS, Orbit of the Earth
January 27, 2017

Image Credit: NASA

Lightning over Texas

Lightning over Texas

Denton, Texas, USA

Image Credit & Copyright: Matthew Clark

Exoplanet Kepler-452b

Exoplanet Kepler-452b

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water -- an essential ingredient for life as we know it -- to pool on the surface. Scientists do not know if Kepler-452b can support life or not. What is known about the planet is that it is about 60 percent larger than Earth, placing it in a class of planets dubbed "super-Earths." While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a better than even chance of being rocky. Kepler-452b orbits its star every 385 days. The planet's star is about 1,400 light-years away in the constellation Cygnus. It is a G2-type star like our sun, with nearly the same temperature and mass. This star is 6 billion years old, 1.5 billion years older than our sun. As stars age, they grow in size and give out more energy, warming up their planets over time.

Image Credit: NASA Ames/JPL-Caltech/T. Pyle
Explanation from: https://www.nasa.gov/image-feature/soaking-up-the-rays-of-a-sun-like-star-artistic-concept

Aurora over Alaska

Aurora over Alaska

This image of a colorful aurora was taken in Delta Junction, Alaska in 2015. All auroras are created by energetic electrons, which rain down from Earth’s magnetic bubble and interact with particles in the upper atmosphere to create glowing lights that stretch across the sky.

Delta Junction, Alaska, USA
2015

Image Credit & Copyright: Sebastian Saarloos

Saturn's moon Dione

Saturn's moon Dione

When viewed from a distance with the sun directly behind Cassini, the larger, brighter craters really stand out on moons like Dione.

Among these larger craters, some leave bright ray patterns across the moon, calling attention to their existence and to the violence of their creation.

The rayed crater seen here on Dione (698 miles, or 1,123 kilometers across) is named Creusa. The rays are brighter material blasted out by the impact that formed the crater. Scientists can use the patterns of ejecta (like these rays), to help determine the order of geological events on a moon's surface by examining which features lie on top of other features.

This view looks toward the Saturn-facing side of Dione. North on Dione is up and rotated 31 degrees to the right. The image was taken with the Cassini spacecraft narrow-angle camera on Nov. 26, 2016 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 727 nanometers.

The view was obtained at a distance of approximately 350,000 miles (560,000 kilometers) from Dione. Image scale is 1.8 miles (3 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA20521

Hot-Lava World: Exoplanet 55 Cancri e

Hot-Lava World: Exoplanet 55 Cancri e

This illustration shows one possible scenario for the hot, rocky exoplanet called 55 Cancri e, which is nearly two times as wide as Earth. New data from NASA's Spitzer Space Telescope show that the planet has extreme temperature swings from one side to the other – and a possible reason for this might be the presence of lava pools.

This planet is tidally locked to its star, just as our moon is to Earth, which means that one side always sizzles under the heat of its star while the other side remains in the dark. If the planet were covered in lava, then the hot, sun-facing side of the planet would have liquid lava flows, while the colder, dark side would see solidified lava rock. The hardened lava would be unable to transport heat across the planet, explaining why Spitzer detected that the cold side of the planet is much colder than the hot side.

Such a lava planet, if it exists, would have dust streaming off of it, as illustrated here. Radiation and winds from the nearby star would blow off the material.

Scientists say that future observations with NASA's upcoming James Webb Space Telescope should provide more details about the nature of this exotic world.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/image-feature/jpl/hot-lava-world-illustration

February 20, 2017

Fallstreak Hole Cloud over Victoria

Fallstreak Hole Cloud over Victoria

Victoria, Australia
November 3, 2014

Image Credit & Copyright: David Barton

Aurora seen from the International Space Station

Aurora seen from the International Space Station

The Expedition 32 crew onboard the International Space Station, flying an altitude of approximately 240 miles, recorded a series of images of Aurora Australis, also known as the Southern Lights, on July 15. NASA astronaut Joe Acaba, flight engineer, recorded the series of images from the Tranquility node. The Canadarm2 robot arm is in the foreground.

ISS, Orbit of the Earth
July 15, 2012

Image Credit: NASA

Spiral Galaxy ESO 121-6

Spiral Galaxy ESO 121-6

This thin, glittering streak of stars is the spiral galaxy ESO 121-6, which lies in the southern constellation of Pictor (The Painter's Easel). Viewed almost exactly side-on, the intricate structure of the swirling arms is hidden, but the full length of the galaxy can be seen — including the intense glow from the central bulge, a dense region of tightly packed young stars sitting at the centre of the spiral arms.

Tendrils of dark dust can be seen across the frame, partially obscuring the bright centre of the galaxy and continuing out towards the smattering of stars at its edges, where the dust lanes and shapes melt into the inky background. Numerous nearby stars and galaxies are visible as small smudges in the surrounding sky, and the brightest stars are dazzlingly prominent towards the bottom left of the image.

ESO 121-6 is a galaxy with patchy, loosely wound arms and a relatively faint central bulge. It actually belongs to a group of galaxies, a clump of no more than 50 similar structures all loosely bound to one another by gravity. The Milky Way is also a member of a galactic group, known as the Local Group.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1305a/

Shiveluch Volcano Eruption

Shiveluch Volcano Eruption

Kamchatka Peninsula, Russia
January 25, 2016

Image Credit: Getty Images

Mars

Mars

About 1000 Viking Orbiter red- and violet-filter images have been processed to provide global color coverage of Mars at a scale of 1 km/pixel. Individual image frames acquired during a single spacecraft revolution were first processed through radiometric calibration, cosmetic cleanup, geometric control, reprojection, and mosaicing. We have produced a total of 57 "single-rev" mosaics. All of the mosaics are geometrically tied to the Mars Digital Image Mosaic, a black-and-white base map with a scale of 231 m/pixel. We selected a subset of single-rev mosaics that provide the best global coverage (least atmospheric obscuration and seasonal frost); photometric normalization was applied to remove atmospheric effects and normalize the variations in illumination and viewing angles.

Finally, these normalized mosaics were combined into global mosaics. Global coverage is about 98% complete in the red-filter mosaic and 95% complete in the violet-filter mosaic. Gaps were filled by interpolation. A green-filter image was synthesized from an average of the red and violet filter data to complete a 3-color set. The Viking Orbiters acquired actual green-filter images for only about half of the Martian surface. The final mosaic has been reprojected into several map projections. The orthographic view shown here is centered at 20 degrees latitude and 60 degrees longitude.

The orthographic view is most like the view seen by a distant observer looking through a telescope. The color balance selected for these images was designed to be close to natural color for the bright reddish regions such as Tharsis and Arabia, but the data have been "stretched" such that the relatively dark regions appear darker and less reddish that their natural appearance. This stretching allows us to better see the color and brightness variations on Mars, which are related to the composition or physical structure of the surface materials, which include volcanic lava flows, wind- and water-deposited sedimentary rocks, and (at the poles) ice caps.

The north polar cap is visible in this projection at the top of the image, the great equatorial canyon system (Valles Marineris) below center, and four huge Tharsis volcanoes (and several smaller ones) at left. Also note heavy impact cratering of the highlands (bottom and right portions of this mosaic) and the younger, less heavily cratered terrains elsewhere.

Image Credit: NASA/JPL/USGS
Explanation from: http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia00407

Search for Exoplanets: Archean Earth

Archean Earth
When haze built up in the atmosphere of Archean Earth, the young planet might have looked like this artist's interpretation - a pale orange dot. A team led by Goddard scientists thinks the haze was self-limiting, cooling the surface by about 36 degrees Fahrenheit (20 Kelvins) – not enough to cause runaway glaciation. The team’s modeling suggests that atmospheric haze might be helpful for identifying earthlike exoplanets that could be habitable.

For astronomers trying to understand which distant planets might have habitable conditions, the role of atmospheric haze has been hazy. To help sort it out, a team of researchers has been looking to Earth – specifically Earth during the Archean era, an epic 1-1/2-billion-year period early in our planet’s history.

Earth’s atmosphere seems to have been quite different then, probably with little available oxygen but high levels of methane, ammonia and other organic chemicals. Geological evidence suggests that haze might have come and gone sporadically from the Archean atmosphere – and researchers aren’t quite sure why. The team reasoned that a better understanding of haze formation during the Archean era might help inform studies of hazy earthlike exoplanets.

“We like to say that Archean Earth is the most alien planet we have geochemical data for,” said Giada Arney of NASA’s Goddard Spaceflight Center in Greenbelt, Maryland, and a member of the NASA Astrobiology Institute’s Virtual Planetary Laboratory based at the University of Washington, Seattle.

In the best case, haze in a planet’s atmosphere could serve up a smorgasbord of carbon-rich, or organic, molecules that could be transformed by chemical reactions into precursor molecules for life. Haze also might screen out much of the harmful UV radiation that can break down DNA.

In the worst case, haze could become so thick that very little light gets through. In this situation, the surface might get so cold it freezes completely. If a very thick haze occurred on Archean Earth, it might have had a profound effect, because when the era began roughly four billion years ago, the sun was fainter, emitting perhaps 80 percent of the light that it does now.

Arney and her colleagues put together sophisticated computer modeling to look at how haze affected the surface temperature of Archean Earth and, in turn, how the temperature influenced the chemistry in the atmosphere.

The new modeling indicates that as the haze got thicker, less sunlight would have gotten through, inhibiting the types of sunlight-driven chemical reactions needed to form more haze. This would lead to the shutdown of haze-formation chemistry, preventing the planet from undergoing runaway glaciation due to a very thick haze.

The team calls this self-limiting haze, and their work is the first to make the case that this is what occurred on Archean Earth – a finding published in the November 2016 issue of the journal Astrobiology. The researchers concluded that self-limiting haze could have cooled Archean Earth by about 36 degrees Fahrenheit (20 Kelvins) – enough to make a difference but not to freeze the surface completely.

“Our modeling suggests that a planet like hazy Archean Earth orbiting a star like the young sun would be cold,” said Shawn Domagal-Goldman, a Goddard scientist and a member of the Virtual Planetary Laboratory. “But we’re saying it would be cold like the Yukon in winter, not cold like modern-day Mars.”

Such a planet might be considered habitable, even if the mean global temperature is below freezing, as long as there is some liquid water on the surface.

In subsequent modeling, Arney and her colleagues looked at the effects of haze on planets that are like Archean Earth but orbiting several kinds of stars.

“The parent star controls whether a haze is more likely to form, and that haze can have multiple impacts on a planet’s habitability,” said co-author Victoria Meadows, the principal investigator for the Virtual Planetary Laboratory and an astronomy professor at the University of Washington.

It looks as if the Archean Earth hit a sweet spot where the haze served as a sunscreen layer for the planet. If the sun had been a bit warmer, as it is today, the modeling suggests the haze particles would have been larger – a result of temperature feedbacks influencing the chemistry – and would have formed more efficiently, but still would have offered some sun protection.

The same wasn’t true in all cases. The modeling showed that some stars produce so much UV radiation that haze cannot form. Haze did not cool planets orbiting all types of stars equally, either, according to the team’s results. Dim stars, such as M dwarfs, emit most of their energy at wavelengths that pass right through atmospheric haze; in the simulations, these planets experience little cooling from haze, so they benefit from haze’s UV shielding without a major drop in temperature.

For the right kind of star, though, the presence of haze in a planet’s atmosphere could help flag that world as a good candidate for closer study. The team’s simulations indicated that, for some instruments planned for future space telescopes, the spectral signature of haze would appear stronger than the signatures for some atmospheric gases, such as methane.

“Haze may turn out to be very helpful as we try to narrow down which exoplanets are the most promising for habitability,” said Arney.

Image Credit: NASA’s Goddard Space Flight Center/Francis Reddy
Explanation from: https://www.nasa.gov/feature/goddard/2017/nasa-team-looks-to-ancient-earth-first-to-study-hazy-exoplanets

February 19, 2017

Supercell, Mammatus Clouds and Lightning over Nebraska

Supercell, Mammatus Clouds and Lightning over Nebraska

Broken Bow, Nebraska, USA
May 26, 2013

Image Credit & Copyright: Weather Studios

Earth and Cygnus spacecraft seen from International Space Station

Earth and Cygnus spacecraft seen from International Space Station

The first Cygnus commercial cargo spacecraft built by Orbital Sciences Corp. is photographed by an Expedition 37 crew member on the International Space Station during rendezvous and docking operations. The two spacecraft converged at 7:01 a.m. EDT on September 29, 2013.

ISS, Orbit of the Earth
September 29, 2013

Image Credit: NASA

Hubble eXtreme Deep Field

Hubble eXtreme Deep Field

Like photographers assembling a portfolio of their best shots, astronomers have assembled a new, improved portrait of our deepest-ever view of the Universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining ten years of NASA/ESA Hubble Space Telescope observations taken of a patch of sky within the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full Moon.

The Hubble Ultra Deep Field is an image of a small area of space in the constellation of Fornax (The Furnace), created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over one million seconds of observation, the resulting image revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the Universe ever taken at that time.

The new full-colour XDF image is even more sensitive than the original Hubble Ultra Deep Field image, thanks to the additional observations, and contains about 5500 galaxies, even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness that the unaided human eye can see.

Magnificent spiral galaxies similar in shape to the Milky Way and its neighbour the Andromeda galaxy appear in this image, as do large, fuzzy red galaxies in which the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years as the stars within them age.

Peppered across the field are tiny, faint, and yet more distant galaxies that are like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like the Milky Way — is laid out in this one remarkable image.

Hubble pointed at a tiny patch of southern sky in repeat visits made over the past decade with a total exposure time of two million seconds. More than 2000 images of the same field were taken with Hubble’s two primary cameras: the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light. These were then combined to form the XDF.

“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before,” said Garth Illingworth of the University of California at Santa Cruz, principal investigator of the Hubble Ultra Deep Field 2009 (HUDF09) programme.

The Universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early Universe was a time of dramatic birth for galaxies containing brilliant blue stars far brighter than our Sun. The light from those past events is just arriving at Earth now, and so the XDF is a time tunnel into the distant past when the Universe was just a fraction of its current age. The youngest galaxy found in the XDF existed just 450 million years after the Universe’s birth in the Big Bang.

Before Hubble was launched in 1990, astronomers were able to see galaxies up to about seven billion light-years away, half way back to the Big Bang. Observations with telescopes on the ground were not able to establish how galaxies formed and evolved in the early Universe.

Hubble gave astronomers their first view of the actual forms of galaxies when they were young. This provided compelling, direct visual evidence that the Universe is truly changing as it ages. Like watching individual frames of a motion picture, the Hubble deep surveys reveal the emergence of structure in the infant Universe and the subsequent dynamic stages of galaxy evolution.

The NASA/ESA/CSA James Webb Space Telescope (Webb telescope), scheduled for launch in 2018, will be aimed at the XDF, and will study it with its infrared vision. The Webb telescope will find even fainter galaxies that existed when the Universe was just a few hundred million years old. Because of the expansion of the Universe, light from the distant past is stretched into longer, infrared wavelengths. The Webb telescope’s infrared vision is ideally suited to push the XDF even deeper, into a time when the first stars and galaxies formed and filled the early “dark ages” of the Universe with light.

Image Credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 TeamExplanation from: https://www.spacetelescope.org/news/heic1214/

Lightning over Sierra Nevada

Lightning over Sierra Nevada

Olancha, California, USA
September 20, 2014

Image Credit & Copyright: Michael Shainblum

Barnard 3

Barnard 3

NASA's Wide-field Infrared Survey Explorer (WISE) mission presents the "Wreath nebula." Though this isn't the nebula's official name (it's actually called Barnard 3, or IRAS Ring G159.6-18.5), one might picture a wreath in these bright green and red dust clouds -- a ring of evergreens donned with a festive red bow, a jaunty sprig of holly, and silver bells throughout. Interstellar clouds like these are stellar nurseries, places where baby stars are being born.

The green ring (evergreen) is made of tiny particles of warm dust whose composition is very similar to smog found here on Earth. The red cloud (bow) in the middle is probably made of dust that is more metallic and cooler than the surrounding regions. The bright star in the middle of the red cloud, called HD 278942, is so luminous that it is likely what is causing most of the surrounding ring to glow. In fact its powerful stellar winds are what cleared out the surrounding warm dust and created the ring-shaped feature in the first place. The bright greenish-yellow region left of center (holly) is similar to the ring, though more dense. The bluish-white stars (silver bells) scattered throughout are stars located both in front of, and behind, the nebula.

Regions similar to this nebula are found near the band of the Milky Way galaxy in the night sky. The "wreath" is slightly off this band, near the boundary between the constellations of Perseus and Taurus, but at a relatively close distance of only about 1,000 light-years, the cloud is a still part of our Milky Way.

The colors used in this image represent specific wavelengths of infrared light. Blue and cyan (blue-green) represent light emitted at wavelengths of 3.4 and 4.6 microns, which is predominantly from stars. Green and red represent light from 12 and 22 microns, respectively, which is mostly emitted by dust.

Image Credit: NASA/JPL-Caltech/UCLA
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA15252

Globular Cluster NGC 6934

Globular Cluster NGC 6934

This bright spray of stars in the small but evocative constellation of Delphinus (the Dolphin) is the globular cluster NGC 6934. Globular clusters are large balls of (typically) a few hundred thousand ancient stars that exist on the edges of galaxies.

Lying 50 000 light-years from Earth, in the outer reaches of our Milky Way galaxy, NGC 6934 is home to some of the most distant stars still to be part of our galactic system — in a sense, it is a far-flung suburb to the Milky Way’s city centre.

NGC 6934 was first seen by William Herschel in the late eighteenth century. He classified it as a “bright nebula” and was not able to resolve it into stars. The cluster is not bright enough to see with the naked eye, and even in ideal conditions it is very difficult to view with binoculars. However, it is a popular target for amateur astronomers as it can easily be observed using relatively inexpensive telescopes. Broadcaster Patrick Moore, presenter of BBC TV’s The Sky at Night for more than 50 years, included this cluster in his “Caldwell catalogue” of celestial objects that amateur astronomers should look out for.

NGC 6934’s faintness is down to its distance — not how bright it really is. With its many thousands of stars, the cluster is no minnow. The fact that the huge core of our galaxy dwarfs it, along with the other 150 or so globular clusters that orbit the Milky Way’s galactic centre, is a reminder of the breathtaking scale of the cosmos.

This picture was taken with the Wide Field Channel of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys. It was created from images taken through filters F814W (near infrared) and F606W (orange), coloured red and blue respectively. The exposure times were 29 minutes per filter, and the field of view is 3.3 arcminutes across.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1023a/