January 27, 2018

Great Dust Storms on Mars

Great Dust Storms on Mars

Two 2001 images from the Mars Orbiter Camera on NASA's Mars Global Surveyor orbiter show a dramatic change in the planet's appearance when haze raised by dust-storm activity in the south became globally distributed.

At left, an image from late June 2001 shows clear conditions over much of the planet, with regional dust-storm activity occurring in the Hellas basin (bright oval feature) near the edge of the south polar cap. At right, a July 2001 image from the same perspective shows the planet almost completely enveloped. Dust extends to altitudes of more than 60 kilometers (37 miles) during global-scale storms.

Although dust storms occur year-round on Mars, they often occur in greater numbers during certain seasons. In particular, it has long been known from Earth-based telescopic observations that the largest, global dust events(those that enshroud the entire planet) occur during the southern spring and summer. As the Mars Global Surveyor (MGS) mission began to monitor this period for the second time, particular attention was paid to local and regional dust storms in anticipation of capturing--for the first time--high spatial-and time-resolution observations of the start of a "global" storm.

Throughout the month of June 2001, the MGS Mars Orbiter Camera (MOC)routinely accumulated low resolution (7.5 km/pixel) global maps of Marson an orbit-by-orbit basis. A moderately large number of local dust storms were noted, especially along the retreating margin of the seasonal south polar CO2 frost cap and around the large and deep Hellas impact basin that dominates the southern, eastern highlands. On June 21, an otherwise undistinguished small dust storm surged into the basin from the southwest. When viewed 24 hours later, the storm had circulated clockwise about 1/3of the circumference of Hellas, indicating relatively high winds. For the next three days, this storm brewed north of Hellas and east towards Hesperia, but didn't cross the equator. Then, sometime between 2 PM local Mars time on June 25 and 2 PM local Mars time on June 26, the storm exploded north across the equator, and in less than 24 hours thereafter, dust was being raised from separate locations in Arabia, Nilosyrtis, and Hesperia, thousands of kilometers away from Hellas. This was the start of the long-anticipated global dust event.

Over the following week, dust injected high into the stratosphere during the initial Hellas and Hesperia storms drifted eastward, carried by the prevailing south circumpolar jet stream. Beneath this "veil" of dust, an intense wind front moved across Mars, setting up conditions for many other local and regional dust storms. By July 4, a large regional storm was raging between Daedalia Planitia south of the Tharsis volcanoes and Syria Planum (just south of Labyrinthus Noctis). Another storm was raising plumes of dust in north central Noachis/southwestern Meridiani. Plumes were rising in Hesperia but not Hellas.

Throughout July and August, MOC observations revealed a general pattern of regional storm centers beneath an ever-spreading veil of stratospheric dust. The Daedalia/Claritas/Syria storm created dust plumes on over 90 consecutive days.

Previous views and perceptions of global dust events had noted regional brightenings within the overall pall of what was called a "global duststorm." From our new observations, we know that at least this global dust "storm" was really a set of storms, somehow triggered to occur at the same time. We also know that dust was not raised from everywhere on the surface during this global event, but rather from discrete, long-lived centers of activity. We saw, for the first time, rapid, cross-equatorial flow of dust-raising winds.

Image Credit: NASA/JPL/MSSS
Explanation from: https://photojournal.jpl.nasa.gov/catalog/pia03170

January 23, 2018

Planetary System Kepler K2-138

Planetary System Kepler K2-138

This artist concept shows K2-138, the first multi-planet system discovered by citizen scientists. The central star is slightly smaller and cooler than our Sun. The five known planets are all between the size of Earth and Neptune. Planet b may potentially be rocky, but planets c, d, e, and f likely contain large amounts of ice and gas. All five planets have orbital periods shorter than 13 days and are all incredibly hot, ranging from 800 to 1,800 degrees Fahrenheit.

Image Credit: NASA/JPL-Caltech
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA22088

January 22, 2018

Star-Forming Region LH 72

Star-Forming Region LH 72

In one of the largest known star formation regions in the Large Magellanic Cloud (LMC), a small satellite galaxy of the Milky Way, lie young and bright stellar groupings known as OB associations. One of these associations, called LH 72, was captured in this dramatic NASA/ESA Hubble Space Telescope image. It consists of a few high-mass, young stars embedded in a beautiful and dense nebula of hydrogen gas.

Much of the star formation in the LMC occurs in super-giant shells. These regions of interstellar gas are thought to have formed due to strong stellar winds and supernova explosions that cleared away much of the material around the stars creating wind-blown shells. The swept-up gas eventually cools down and fragments into smaller clouds that dot the edges of these regions and eventually collapse to form new stars.

The biggest of these shells, home to LH 72, is designated LMC4. With a diameter of about 6000 light-years, it is the largest in the Local Group of galaxies that is home to both the Milky Way and LMC. Studying gas-embedded young associations of stars like LH 72 is a way of probing the super-giant shells to understand how they formed and evolved.

This image was taken with Hubble’s Wide Field Planetary Camera 2 using five different filters in ultraviolet, visible and infrared light. The field of view is approximately 1.8 by 1.8 arcminutes.

Image Credit: ESA/Hubble, NASA and D. A. Gouliermis
Explanation from: https://www.spacetelescope.org/images/potw1147a/

January 21, 2018

Volcán de Colima Eruption

Volcán de Colima Eruption

Colima, Mexico
January 26, 2017

Image Credit & Copyright: Sergio Tapiro