Colliding Atmospheres: Comet C/2013 A1 Siding Spring vs Mars - Video

Incoming: NEOWise spies Comet A1 Siding Spring in early August of 2014. Credit: NASA

This week, the skies over Mars will also be graced by an unforgettable and spectacular sight: the extremely close passage of Comet C/2013 A1 Siding Spring.

The first comet discovered in 2013, A1 Siding Spring was spotted by veteran comet hunter Robert McNaught from the Siding Spring Observatory in Australia.

Dozens of comets are discovered in any given year, but this one soon gained the attention of astronomers when it was found that the comet could possibly hit Mars in October 2014.

And although further observations refined A1 Siding Spring's orbit and ruled out such an impact, the particulars of the close passage of the comet past Mars are still stunning: A1 Siding Spring will pass within 87,000 miles (139,500 kilometres) from the center of Mars on Sunday, October 19th at 18:27 Universal Time (UT) or 2:27 PM EDT.

And although we've yet to set "boots" on Mars, a fleet of spacecraft arrayed throughout the inner solar system are set to study the comet from both near and far.



NASA has taken measures to assure that spacecraft in orbit are afforded maximum protection from incoming cometary debris, and the exciting possibility exists that we'll be able to study first-hand the interaction of the comet's tail with the Martian atmosphere.

Mars-based spacecraft set to observe Comet A1 Siding Spring: a scorecard. 

Credit: NASA

The nucleus of A1 Siding Spring is thought to be 700 metres across, and the coma extends 19,300 km in diameter.

The comet's closest passage is just under six times the distance of Mars' outer moon Deimos, and at closest approach, the coma will appear almost 8 degrees in size to any would-be Martian, that's 16 times the diameter of a Full Moon as seen from the Earth, and will be crossing the skies at a staggering 1.5 degrees a minute.

You would be able to easily see the motion of the comet as it moves across the Martian sky with the unaided eye after just a few dozen seconds worth of watching!

The comet's magnitude may reach -5 as seen from Mars, though that would also be extended over its huge expanded surface area.

A violent, complex scene of colliding galaxy clusters

Colliding galaxy clusters MACS J0717+3745, more than 5 billion light-years from Earth. Background is Hubble Space Telescope image; blue is X-ray image from Chandra, and red is VLA radio image. 

Credit: Van Weeren, et al.; Bill Saxton, NRAO /AUI /NSF; NASA.

Astronomers using the Karl G. Jansky Very Large Array (VLA) and the Chandra X-Ray Observatory have produced a spectacular image revealing new details of violent collisions involving at least four clusters of galaxies.

Combined with an earlier image from NASA's Hubble Space Telescope (HST), the new observations show a complex region more than 5 billion light-years from Earth where the collisions are triggering a host of phenomena that scientists still are working to understand.

The HST image forms the background of this composite, with the X-ray emission detected by Chandra in blue and radio emission seen by the VLA in red.

The X-rays indicate hot, tenuous gas that pervades the region containing the galaxy clusters.

The large, oddly-shaped red feature at the center probably is a region where shocks caused by the collisions are accelerating particles that then interact with magnetic fields and emit the radio waves.

"The complex shape of this region is unique; we've never spotted anything like this before," said Reinout van Weeren, an Einstein Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

"The shape probably is the result of the multiple ongoing collisions," he added.

The new radio and X-ray observations are much more sensitive than previous ones, the scientists said. The combination of these images will make this region one of the best-studied examples of cluster-cluster collisions yet known, and can yield new insights on the complex interactions during cluster mergers.

Together, the merging clusters are called MACS J0717+3745, which also is one of the HST Frontier Fields for which HST will produce the deepest observations ever.

The scientists presented their findings to the American Astronomical Society's meeting in Boston, Mass.

The straight, elongated radio-emitting object is a foreground galaxy whose central black hole is accelerating jets of particles in two directions. The red object at bottom-left is a radio galaxy that probably is falling into the cluster.

NASA Casini Observes Meteors Colliding With Saturn's Rings

Five images of Saturn's rings, taken by NASA's Cassini spacecraft between 2009 and 2012, show clouds of material ejected from impacts of small objects into the rings. 

Image credit: NASA/JPL-Caltech /Space Science Institute/Cornell

NASA's Cassini spacecraft has provided the first direct evidence of small meteoroids breaking into streams of rubble and crashing into Saturn's rings.

These observations make Saturn's rings the only location besides Earth, the moon and Jupiter where scientists and amateur astronomers have been able to observe impacts as they occur.

Studying the impact rate of meteoroids from outside the Saturnian system helps scientists understand how different planet systems in our solar system formed.

The solar system is full of small, speeding objects. These objects frequently pummel planetary bodies. The meteoroids at Saturn are estimated to range from about one-half inch to several yards (1 centimeter to several meters) in size.

It took scientists years to distinguish tracks left by nine meteoroids in 2005, 2009 and 2012.

Details of the observations appear in a paper in the Thursday, April 25 edition of Science.

Results from Cassini have already shown Saturn's rings act as very effective detectors of many kinds of surrounding phenomena, including the interior structure of the planet and the orbits of its moons.

Linda Spilker

For example, a subtle but extensive corrugation that ripples 12,000 miles (19,000 kilometers) across the innermost rings tells of a very large meteoroid impact in 1983.

"These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth -- two very different neighborhoods in our solar system -- and this is exciting to see," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"It took Saturn's rings acting like a giant meteoroid detector -- 100 times the surface area of the Earth -- and Cassini's long-term tour of the Saturn system to address this question."

The Saturnian equinox in summer 2009 was an especially good time to see the debris left by meteoroid impacts.

Matt Tiscareno

The very shallow sun angle on the rings caused the clouds of debris to look bright against the darkened rings in pictures from Cassini's imaging science subsystem.

"We knew these little impacts were constantly occurring, but we didn't know how big or how frequent they might be, and we didn't necessarily expect them to take the form of spectacular shearing clouds," said Matt Tiscareno, lead author of the paper and a Cassini participating scientist at Cornell University in Ithaca, N.Y.

"The sunlight shining edge-on to the rings at the Saturnian equinox acted like an anti-cloaking device, so these usually invisible features became plain to see."

Read the full article here