Sivan 2 to M31

From within the boundaries of the constellation Cassiopeia (left) to Andromeda (right), this telescopic mosaic spans over 10 degrees in planet Earth's skies. The celestial scene is constructed of panels that are part of a high-resolution astronomical survey of the Milky Way in hydrogen-alpha light. Processing the monochromatic image data has brought out the region's faintest structures, relatively unexplored filaments of hydrogen gas near the plane of our Milky Way Galaxy. Large but faint and also relatively unknown nebula Sivan 2 is at the upper left in the field. The nearby Andromeda Galaxy, M31, is at center right, while the faint, pervasive hydrogen nebulosities stretch towards M31 across the foreground in the wide field of view. The broad survey image demonstrates the intriguing faint hydrogen clouds recently imaged by astronomer Rogelio Bernal Andreo really are within the Milky Way, along the line-of-sight to the Andromeda Galaxy.

Sivan 2 to M31 

Image Credit & Copyright: MDW Sky Survey (David Mittelman, Dennis di Cicco, Sean Walker)

Orbiter Steers Clear of Mars Moon Phobos

NASA’s MAVEN spacecraft performed a previously unscheduled maneuver this week to avoid a collision in the near future with Mars’ moon Phobos.
The Mars Atmosphere and VolatileEvolutioN (MAVEN)spacecraft has been orbiting Mars for just over two years, studying the Red Planet’s upper atmosphere, ionosphere and interactions with the sun and solar wind. On Tuesday the spacecraft carried out a rocket motor burn that boosted its velocity by 0.4 meters per second (less than 1 mile per hour). Although a small correction, it was enough that -- projected to one week later when the collision would otherwise have occurred -- MAVEN would miss the lumpy, crater-filled moon by about 2.5 minutes.

This is the first collision avoidance maneuver that the MAVEN spacecraft has performed at Mars to steer clear of Phobos. The orbits of both MAVEN and Phobos are known well enough that this timing difference ensures that they will not collide.

MAVEN, with an elliptical orbit around Mars, has an orbit that crosses those of other spacecraft and the moon Phobos many times over the course of a year.  When the orbits cross, the objects have the possibility of colliding if they arrive at that intersection at the same time. These scenarios are known well in advance and are carefully monitored by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, which sounded the alert regarding the possibility of a collision.

With one week’s advance notice, it looked like MAVEN and Phobos had a good chance of hitting each other on Monday, March 6, arriving at their orbit crossing point within about 7 seconds of each other. Given Phobos’ size (modeled for simplicity as a 30-kilometer sphere, a bit larger than the actual moon in order to be conservative), they had a high probability of colliding if no action were taken.

Said MAVEN Principal Investigator Bruce Jakosky of the University of Colorado in Boulder, “Kudos to the JPL navigation and tracking teams for watching out for possible collisions every day of the year, and to the MAVEN spacecraft team for carrying out the maneuver flawlessly.”

Titan: Send in the Clouds

Floating high above the hydrocarbon lakes, wispy clouds have finally started to return to Titan's northern latitudes.

Clouds like these disappeared from Titan's (3,200 miles or 5,150 kilometers across) northern reaches for several years (from about 2010 to 2014). Now they have returned, but in far smaller numbers than expected. Since clouds can quickly appear and disappear, Cassini scientists regularly monitor the large moon, in the hopes of observing cloud activity. They are especially interested in comparing these observations to predictions of how cloud cover should change with Saturn’s seasons. Titan’s clear skies are not what researchers expected.

This view looks toward the Saturn-facing side of Titan. North on Titan is up and rotated 3 degrees to the left. The image was taken with the Cassini spacecraft narrow-angle camera on Oct. 29, 2016 using a spectral filter that preferentially admits wavelengths of near-infrared light centered at 938 nanometers.

The view was obtained at a distance of approximately 545,000 miles (878,000 kilometers) from Titan. Image scale is 3 miles (5 kilometers) per pixel.