Hubble Provides Interstellar Road Map for Voyagers’ Galactic Trek

In this artist's conception, NASA's Voyager 1 spacecraft has a bird's-eye view of the solar system. The circles represent the orbits of the major outer planets: Jupiter, Saturn, Uranus, and Neptune. Launched in 1977, Voyager 1 visited the planets Jupiter and Saturn. The spacecraft is now 13 billion miles from Earth, making it the farthest and fastest-moving human-made object ever built. In fact, Voyager 1 is now zooming through interstellar space, the region between the stars that is filled with gas, dust, and material recycled from dying stars.

NASA’s two Voyager spacecraft are hurtling through unexplored territory on their road trip beyond our solar system. Along the way, they are measuring the interstellar medium, the mysterious environment between stars. NASA’s Hubble Space Telescope is providing the road map – by measuring the material along the probes’ future trajectories. Even after the Voyagers run out of electrical power and are unable to send back new data, which may happen in about a decade, astronomers can use Hubble observations to characterize the environment of through which these silent ambassadors will glide.

A preliminary analysis of the Hubble observations reveals a rich, complex interstellar ecology, containing multiple clouds of hydrogen laced with other elements. Hubble data, combined with the Voyagers, have also provided new insights into how our Sun travels through interstellar space.

In this illustration oriented along the ecliptic plane, NASA's Hubble Space Telescope looks along the paths of NASA's Voyager 1 and 2 spacecraft as they journey through the solar system and into interstellar space. Hubble is gazing at two sight lines (the twin cone-shaped features) along each spacecraft's path. The telescope's goal is to help astronomers map interstellar structure along each spacecraft's star-bound route. Each sight line stretches several light-years to nearby stars.

“This is a great opportunity to compare data from in situ measurements of the space environment by the Voyager spacecraft and telescopic measurements by Hubble,” said study leader Seth Redfield of Wesleyan University in Middletown, Connecticut. “The Voyagers are sampling tiny regions as they plow through space at roughly 38,000 miles per hour. But we have no idea if these small areas are typical or rare. The Hubble observations give us a broader view because the telescope is looking along a longer and wider path. So Hubble gives context to what each Voyager is passing through.”

The astronomers hope that the Hubble observations will help them characterize the physical properties of the local interstellar medium. “Ideally, synthesizing these insights with in situ measurements from Voyager would provide an unprecedented overview of the local interstellar environment,” said Hubble team member Julia Zachary of Wesleyan University.

NASA launched the twin Voyager 1 and 2 spacecraft in 1977. Both explored the outer planets Jupiter and Saturn. Voyager 2 went on to visit Uranus and Neptune.

The pioneering Voyager spacecraft are currently exploring the outermost edge of the Sun’s domain . Voyager 1 is now zooming through interstellar space, the region between the stars that is filled with gas, dust, and material recycled from dying stars.

Voyager 1 is 13 billion miles from Earth, making it the farthest human-made object ever built. In about 40,000 years, after the spacecraft will no longer be operational and will not be able to gather new data, it will pass within 1.6 light-years of the star Gliese 445, in the constellation Camelopardalis. Its twin, Voyager 2, is 10.5 billion miles from Earth, and will pass 1.7 light-years from the star Ross 248 in about 40,000 years.

For the next 10 years, the Voyagers will be making measurements of interstellar material, magnetic fields and cosmic rays along their trajectories. Hubble complements the Voyagers’ observations by gazing at two sight lines along each spacecraft’s path to map interstellar structure along their star-bound routes. Each sight line stretched several light-years to nearby stars. Sampling the light from those stars, Hubble’s Space Telescope Imaging Spectrograph measures how interstellar material absorbs some of the starlight, leaving telltale spectral fingerprints.

Hubble found that Voyager 2 will move out of the interstellar cloud that surrounds the solar system in a couple thousand years. The astronomers, based on Hubble data, predict that the spacecraft will spend 90,000 years in a second cloud and pass into a third interstellar cloud.

An inventory of the clouds’ composition reveals slight variations in the abundances of the chemical elements contained in the structures. “These variations could mean the clouds formed in different ways, or from different areas, and then came together,” Redfield said.

An initial look at the Hubble data also suggests that the Sun is passing through clumpier material in nearby space, which may affect the heliosphere, the large bubble containing our solar system that is produced by our Sun’s powerful solar wind. At its boundary, called the heliopause, the solar wind pushes outward against the interstellar medium. Hubble and Voyager 1 made measurements of the interstellar environment beyond this boundary, where the wind comes from stars other than our Sun.

“I’m really intrigued by the interaction between stars and the interstellar environment,” Redfield said. “These kinds of interactions are happening around most stars, and it is a dynamic process.”

The heliosphere is compressed when the Sun moves through dense material, but it expands back out when the star passes through low-density matter. This expansion and contraction is caused by the interaction between the outward pressure of the stellar wind, composed of a stream of charged particles, and the pressure of the interstellar material surrounding a star.

Image Credit: X-ray: NASA, ESA, G. Bacon (STScI). Z. Levay (STScI)
Explanation from: https://www.nasa.gov/feature/goddard/2017/hubble-provides-interstellar-road-map-for-voyagers-galactic-trek

Hubble Detects ‘Exocomets’ Taking the Plunge Into a Young Star

This illustration shows several comets speeding across a vast protoplanetary disk of gas and dust and heading straight for the youthful, central star. These "kamikaze" comets will eventually plunge into the star and vaporize. The comets are too small to photograph, but their gaseous spectral "fingerprints" on the star's light were detected by NASA's Hubble Space Telescope. The gravitational influence of a suspected Jupiter-sized planet in the foreground may have catapulted the comets into the star. This star, called HD 172555, represents the third extrasolar system where astronomers have detected doomed, wayward comets. The star resides 95 light-years from Earth.

Interstellar forecast for a nearby star: Raining comets! NASA’s Hubble Space Telescope has discovered comets plunging onto the star HD 172555, which is a youthful 23 million years old and resides 95 light-years from Earth.

The exocomets — comets outside our solar system — were not directly seen around the star, but their presence was inferred by detecting gas that is likely the vaporized remnants of their icy nuclei.

HD 172555 represents the third extrasolar system where astronomers have detected doomed, wayward comets. All of the systems are young, under 40 million years old.

The presence of these doomed comets provides circumstantial evidence for “gravitational stirring” by an unseen Jupiter-size planet, where comets deflected by its gravity are catapulted into the star. These events also provide new insights into the past and present activity of comets in our solar system. It’s a mechanism where infalling comets could have transported water to Earth and the other inner planets of our solar system.

Astronomers have found similar plunges in our own solar system. Sun-grazing comets routinely fall into our sun. “Seeing these sun-grazing comets in our solar system and in three extrasolar systems means that this activity may be common in young star systems,” said study leader Carol Grady of Eureka Scientific Inc. in Oakland, California, and NASA's Goddard Spaceflight Center in Greenbelt, Maryland. “This activity at its peak represents a star’s active teenage years. Watching these events gives us insight into what probably went on in the early days of our solar system, when comets were pelting the inner solar system bodies, including Earth. In fact, these star-grazing comets may make life possible, because they carry water and other life-forming elements, such as carbon, to terrestrial planets.”

The star is part of the Beta Pictoris Moving Group, a collection of stars born from the same stellar nursery. It is the second group member found to harbor such comets. Beta Pictoris, the group’s namesake, also is feasting on exocomets travelling too close. A young gas-giant planet has been observed in that star’s vast debris disk.

The stellar group is important to study because it is the closest collection of young stars to Earth. At least 37.5 percent of the more massive stars in the Beta Pictoris Moving Group either have a directly imaged planet, such as 51 Eridani b in the 51 Eridani system, or infalling star-grazing bodies, or, in the case of Beta Pictoris, both types of objects. The grouping is at about the age that it should be building terrestrial planets, Grady said.

A team of French astronomers first discovered exocomets transiting HD 172555 in archival data gathered between 2004 and 2011 by the European Southern Observatory’s HARPS (High Accuracy Radial velocity Planet Searcher) planet-finding spectrograph. A spectrograph divides light into its component colors, allowing astronomers to detect an object’s chemical makeup. The HARPS spectrograph detected the chemical fingerprints of calcium imprinted in the starlight, evidence that comet-like objects were falling into the star.

As a follow-up to that discovery, Grady’s team used Hubble’s Space Telescope Imaging Spectrograph (STIS) and the Cosmic Origins Spectrograph (COS) in 2015 to conduct a spectrographic analysis in ultraviolet light, which allows Hubble to identify the signature of certain elements. Hubble made two observations, separated by six days.

Hubble detected silicon and carbon gas in the starlight. The gas was moving at about 360,000 miles per hour across the face of the star. The most likely explanation for the speedy gas is that Hubble is seeing material from comet-like objects that broke apart after streaking across the face of the star.

The gaseous debris from the disintegrating comets is vastly dispersed in front of the star. “As transiting features go, this vaporized material is easy to see because it contains very large structures,” Grady said. “This is in marked contrast to trying to find a small transiting exoplanet, where you’re looking for tiny dips in the star’s light.”

Hubble gleaned this information because the HD 172555 debris disk surrounding the star is slightly inclined to Hubble’s line of sight, giving the telescope a clear view of comet activity.

Grady’s team hopes to use STIS again in follow-up observations to look for oxygen and hydrogen, which would confirm the identity of the disintegrating objects as comets.

“Hubble shows that these star-grazers look and move like comets, but until we determine their composition, we cannot confirm they are comets,” Grady said. “We need additional data to establish whether our star-grazers are icy like comets or more rocky like asteroids.”

Image Credit: NASA, ESA, A. Feild and G. Bacon (STScI)
Explanation from: https://www.nasa.gov/feature/goddard/2017/hubble-detects-exocomets-taking-the-plunge-into-a-young-star

Earth and the International Space Station

The International Space Station seen from Space Shuttle Discovery as the two spacecraft undocked. Earlier the STS-128 and Expedition 20 crew concluded nine days of work on the Shuttle and Station. Undocking of the two spacecraft occurred at 21:26 CEST on 8 September 2009.

Image Credit: NASA