Comet A1 Siding Spring vs Mars: Views in Space and Time


Oh, to be a stranded astronaut on the surface of the planet Mars this week.  There’s a great scene from Andy Weir’s recent novel The Martian where chief protagonist Mark Watney uses the swift moving moons of Phobos and Deimos to roughly gauge his direction while travelling across the expansive Martian desert.

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.

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

Universe Today has written extensively on the scientific efforts to study the event, how to observe the comet from Earth, and the unprecedented amateur and professional campaign in progress to witness the close pass.

What we’d like to do now is imagine the unparalleled view under alien skies as the comet slides gracefully overhead.

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 (well, space suit helmet protected) 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.

The enormous tail of the comet would also span the sky, and NASA has already released several mind blowing simulations to this effect.  We’ve also constructed some brief simulations using Starry Night that show the view of the encounter from Earth, Phobos, and the perspective from the comet itself:

There’s also been some discussion as of late that A1 Siding Spring has slowed down in terms of its predicted brightening, though this is not unusual or unexpected.

From Acidalia Planitia (the setting for The Martian) located in the mid-northern latitudes on the surface of Mars, the comet would be a fine morning object, sitting 48 degrees above the northeastern horizon at dawn at closest passage for one morning only, and perhaps staying visible even after sunrise. Earth would be in the picture too, shining at magnitude -2.5 in the Martian dawn.

Dawn on  October 19th, 2014, as seen from Mars. Created using Starry Night.

And the view from the comet?  Now that would be a truly spectacular ride, as Mars swells to 3 degrees in diameter as it approaches and recedes. The comet itself is on a million year plus orbit, never to again visit the realm of the inner solar system in our lifetimes.

Such a view has never been seen in recorded history from the Earth. The closest confirmed passage of a large comet near our planet was Comet D/1770 L1 Lexell, which passed over 15 times more distant than A1 Siding Spring from Mars, at 2.2 million km from Earth on July 1st, 1770. Note that an even closer cometary passage in 1491 remains unverified. In more recent times, Comet Hyakutake passed 15.8 million km from Earth on March 25th, 1996, with a tail that spanned half the sky as seen from a dark sky site, and long-time comet observers might also remember the 1983 passage of Comet IRAS-Araki-Alcock, which passed just 4.7 million kilometres from the Earth.

A1 Siding Spring imaged from Earth on October 11th, 2014. Credit: Efrain Morales Rivera.

And then there was the historic impact on Comet Shoemaker-Levy 9 into Jupiter in 1994, reminding us that cosmic catastrophes can and do indeed occur… the upper size limit estimate for the nucleus of A1 Siding Spring compares to 70% the size of Fragment G, and an impact on Earth or Mars of such a dirty snowball would be a very bad day, for rovers or the humans. An extinction level event such as the Chicxulub impactor, however, was estimated to be much larger, at about 10 km in size.

A1 Siding Springs as imaged on September 3rd, 2014. Credit: Roger Hutchinson.

Thankfully, we’ve merely got a front row seat to the show this weekend, and our planet is not the main event. From Earth, Comet A1 Siding Spring will be a binocular object, shining at magnitude +9 as it passes 3’ from +0.9 magnitude Mars. Both will be visible briefly in dusk skies, and the Virtual Telescope Project also plans to broadcast the event live starting at 16:45 UT on October 19th.

Don’t miss the historic passage of Comet A1 Siding Spring past Mars… by this time next week, we fully expect more images of the comet — both amateur and professional — to grace the cyber-pages of Universe Today!

  • Imaging A1 Siding Spring and/or Mars? Send those astro-pics into Universe Today at our Flickr forum.

Interesting Prospects for Comet A1 Siding Spring Versus the Martian Atmosphere

Inbound: the Hubble Space Telescope images Comet 2013 A1 Siding Spring with its Wide Field Camera 3. Credit: NASA.

It may be the chance of a lifetime for planetary science.

This October, a comet will brush past a planet, giving scientists a chance to study how it possibly interacts with a planetary atmosphere.

The comet is C/2013 A1 Siding Spring, and the planet in question Mars.  And although an impact of the comet on the surface of the Red Planet has long been ruled out, a paper in the May 2014 issue of Icarus raises the interesting possibility of possible interactions of the coma of A1 Siding Spring and the tenuous atmosphere of Mars. The study comes out of the Department of Planetary Sciences at the University of Arizona, the Belgian Institute for Space Aeronomy, the Institut de Planétologie et d’Astrophysique de Grenoble at the Université J. Fourier in France, and the Cooperative Institute for Research in Environmental Sciences at the University of Colorado in Boulder.

For the study, researchers considered how active Comet A1 Siding Spring may be at the time of closest approach on October 19th, 2014.

Discovered early last year by Robert McNaught from the Siding Spring Observatory in Australia, Comet A1 Siding Spring created a stir in the astronomical community when it was found that it will pass extremely close to Mars later this year. Further measurements of its orbit have since ruled this possibility out, but its passage will still be a close one, with a nominal passage of 138,000 kilometres from Mars. That’s about one third the distance from Earth to the Moon, and 17 times closer than the nearest recorded passage of a comet to the Earth, Comet D/1770 L1 Lexell in 1780. Mars’ outer moon Deimos has an orbital distance of about 23,500 kilometres.

The passage of Comet 2013 A1 Siding Spring through the inner solar system. Credit: NASA.
The passage of Comet 2013 A1 Siding Spring through the inner solar system. Credit: NASA.

And although the nucleus will safely pass Mars, the brush with its extended atmosphere might just be detectable by the fleet of spacecraft and rovers in service around Mars. At a distance of 1.4 Astronomical Units (A.U.) from the Sun during the encounter, the vast coma is expected to be comprised primarily of H2O. At an input angle of about 60 degrees, penetration was calculated in the study to impinge down and altitude of 154 kilometres to the topside of the Martian ionosphere, in the middle of the thermosphere.

Such an effect should linger for just over 4 hours, well over the interaction period of Mars’ atmosphere with the coma of just over an hour, centered on 18:30 UT on October 19th, 2014.

What kind of views might missions like HiRISE and MSL get of the comet remains to be seen, although NEOWISE and Hubble are already monitoring the comet for enhanced activity. The Opportunity rover is also still functioning, and Mars Odyssey and ESA’s Mars Express are still in orbit around the Red Planet and sending back data. But perhaps the most interesting possibilities for observations of the event are still en route: India’s Mars Orbiter Mission and NASA’s MAVEN orbiter arrive just before the comet. MAVEN was designed to study the upper atmosphere of Mars, and carries an ion-neutral mass spectrometer (NGIMS) which could yield information on the interaction of the coma with the Martian upper atmosphere and ionosphere. The NGIMS cover is slated for release just two days before the comet encounter. All spacecraft orbiting Mars may feel the increased drag effects of the encounter.

A simulation of Mars as seen from Comet A1 Siding Spring on closest approach. Created by the author using Starry Night Software.
A simulation of Mars as seen from Comet A1 Siding Spring on closest approach. Created by the author using Starry Night Software.

Proposals for using Earth-based assets for further observations of the comet prior to the event in October are still pending.  Amateur observers will be able to follow the approach telescopically, as Comet A1 Siding Spring is expected to reach +8th magnitude in October and pass 7’ from Mars in the constellation Ophiuchus as seen from the Earth. Mars just passed opposition last month, but both will be low to the south west at dusk for northern hemisphere observers in October.

It’s also interesting to consider the potential for interactions of the coma with the surfaces of the moons of Mars as well, though the net amount of water vapor expected to be deposited will not be large.

UPDATE: Check out this nifty interactive simulator which includes Comet A1 Siding Springs courtesy of the Solar System Scope:

The H2O coma of A1 Siding Spring is expected to have a radius of 150,000 kilometres when it passes Mars, just a shade over the nominal flyby distance.

“There is a more extended coma made up of H2O dissociation products (such as hydrogen and hydroxide) that extends for ~1,000,000 kilometres,” researcher at the Department of Planetary Sciences at the University of Arizona and lead author on the paper Roger Yelle told Universe Today.

“Essentially, Mars is in the outer reaches of the coma. The main ion tail misses Mars but there will be some ions from the comet that do reach Mars. The dust tail just misses Mars, which is fortunate.”

The paper also notes that significant perturbations of the upper atmosphere of Mars will occur if the cometary production rate is 10^28 s-1 or larger, which corresponds to about 300 kilograms per second.

“The MAVEN spacecraft will make very interesting observations,” Roger Yelle also told Universe Today. “The comet will perturb primarily the upper atmosphere of Mars and MAVEN was designed to study the upper atmosphere of Mars. Also, it’s just such an incredible coincidence that the comet arrives at Mars less than one month after MAVEN does. MAVEN is nominally in its checkout phase then, and the main science phase of the mission was not scheduled to start until November 1st. However, we are reassessing our plans to see what observations we can make. It’s all quite exciting, and we have to balance safety and the desire to make the best science measurements.”

It’s an unprecedented opportunity, that’s for sure… all eyes will be on the planet Mars and Comet A1 Siding Spring on October the 19th!


Space Science Stories to Watch in 2014

Orion moves towards its first EFT-1 spaceflight later this year. (Credit: NASA).

There’s an old Chinese proverb that says, “May you live in interesting times,” and 2013 certainly fit the bill in the world of spaceflight and space science. The past year saw spacecraft depart for Mars, China land a rover on the Moon, and drama in low Earth orbit to repair the International Space Station. And all of this occurred against a landscape of dwindling budgets, government shutdowns that threatened launches and scientific research, and ongoing sequestration.

But it’s a brave new world out there. Here are just a few space-related stories that we’ll watching in 2014:

An artist's conception of ESA's Rosetta and Philae spacecraft approaching comet 67P/Churyumov-Gerasimenko. (Credit: ESA-J. Huart, 2013)
An artist’s conception of ESA’s Rosetta and Philae spacecraft approaching comet 67P/Churyumov-Gerasimenko. (Credit: ESA-J. Huart, 2013)

Rosetta to Explore a Comet: On January 20, 2014, the European Space Agency will hail its Rosetta spacecraft and awaken it for its historic encounter with comet 67P/Churyumov-Gerasimenko later this year in August. After examining the comet in detail, Rosetta will then dispatch its Philae lander, equipped complete with harpoons and ice screws to make the first ever landing on a comet. Launched way back in 2004, Rosetta promises to provide the cosmic encounter of the year.

The October 19th, 2014 passage of comet C/2013 A1 Siding Springs past Mars. (Credit: NASA/JPL-Caltech)
The October 19th, 2014 passage of comet C/2013 A1 Siding Springs past Mars. (Credit: NASA/JPL-Caltech)

A1 Siding Springs vs. Mars: A comet discovery back in 2013 created a brief stir when researchers noted that comet C/2013 A1 Siding Springs would make a very close passage of the planet Mars on October 19th, 2014. Though refinements from subsequent observations have effectively ruled out the chance of impact, the comet will still pass 41,300 kilometres from the Red Planet, just outside the orbit of its outer moon Deimos. Ground-based observers will get to watch the +7th magnitude comet close in on Mars through October, as will a fleet of spacecraft both on and above the Martian surface.

A recent tweet from @NewHorizons_2015, a spacecraft that launched just weeks before Twitter in 2006.
A recent tweet from @NewHorizons_2015, a spacecraft that, ironically, launched just weeks before Twitter in 2006.

Spacecraft En Route to Destinations: Though no new interplanetary missions are set to depart the Earth in 2014, there are lots of exciting missions currently underway and headed for worlds yet to be explored. NASA’s Dawn spacecraft is headed towards its encounter with 1 Ceres in February 2015. Juno is fresh off its 2013 flyby of the Earth and headed for orbital insertion around Jupiter in August 2016. And in November of this year, New Horizons will switch on permanently for its historic encounter with Pluto and its retinue of moons in July 2015.    

LUX & the Hunt for Dark Matter: It’s all around us, makes up the bulk of the mass budget of the universe, and its detection is THE name of the game in modern astrophysics. But just what is dark matter? Some tantalizing– and hotly contested –data came out late last year from of an unusual detector deep underground near Lead, South Dakota. The Large Underground Xenon experiment (LUX) looks for Weakly Interacting Massive Particles (WIMPs) interacting with 370 kilograms of super-cooled liquid Xenon. LUX requires its unique locale to block out interference from incoming cosmic rays. LUX is due to start another 300 day test run in 2014, and the experiment will add another piece to the puzzle posed by dark matter to modern cosmology, whether or not detections by LUX prove to be conclusive.   

The LIGO Livingston Observatory. (Photos by Author)
The LIGO Livingston Observatory. (Photos by Author)

 The Hunt for Gravity Waves: Another story to watch may come out of Caltech’s twin gravity wave observatories when its Advanced LIGO system goes online later this year. Established in 2002, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is comprised of two detectors: one in Hanford Washington and one outside of Livingston, Louisiana. The detectors look for gravity waves generated by merging binary pulsars and black holes. Though no positive detections have yet been made, Advanced LIGO with boast ten times the sensitivity and may pave the way for a new era of gravitational wave astronomy.

An artist concept of MAVEN in orbit around Mars. (Credit: NASA's Goddard Spaceflight Center).
An artist concept of MAVEN in orbit around Mars. (Credit: NASA’s Goddard Spaceflight Center).

 Spacecraft reach Mars: 2014 is an opposition year for the Red Planet, and with it, two new missions are slated to begin operations around Mars: India’s Mars Orbiter Mission (MOM) also known as Mangalyaan-1 is slated to enter orbit on September 24th, and NASA’s MAVEN or Mars Atmosphere and Volatile Evolution Mission is set to arrive just 2 days earlier on September 22nd. MOM and MAVEN will join the Curiosity and Opportunity rovers, ESA’s Mars Express,  NASA’s Odyssey spacecraft and  the Mars Reconnaissance Orbiter in the quest to unlock the secrets of the Red Planet.

Space Tourism Takes Off: Virgin Galactic’s SpaceShipTwo passed a key milestone test flight in late 2013. Early 2014 may see the first inaugural flights by Virgin Galactic out of the Mohave Spaceport and the start of sub-orbital space tourism. SpaceShipTwo will carry two pilots and six passengers, with seats going for $250,000 a pop. Hey, room for any space journalists in there? On standby, maybe?

The First Flight of Orion: No, it’s not the first flight of the proposed sub-light interplanetary spacecraft that was to be propelled by atomic bombs… but the September launch of the Orion Multi-Purpose Crew Vehicle is the first step in replacing NASA’s capability to launch crews into space. Exploration Flight Test 1 (EFT-1) will be a  short uncrewed flight and test the capsule during reentry after two orbits. It’s to be seen if the first lunar orbital mission using an Orion MPCV will occur by the end of the decade.

Launch of the SpaceX CRS-2 mission to the ISS in early 2013. (Photo by author).
Launch of the SpaceX CRS-2 mission to the ISS in early 2013. (Photo by author)

 The First Flight of the Falcon Heavy: 2014 will be a busy year for SpaceX, starting with the launch of Thaicom-6 out of Cape Canaveral this Friday on January 3rd. SpaceX is now “open for business,” and expect to see them conducting more satellite deployments for customers and resupply missions to the International Space Station in the coming year. They’ll also be moving ahead with tests of their crew-rated version of the Dragon capsule in 2014. But one of the most interesting missions to watch for is the demo flight of the Falcon 9 Heavy slated to launch out of Vandenberg Air Force Base by the end of 2014.… more to come!

The Sunjammer Space Sail: An interesting mission moves in 2014 towards a January 2015 launch: LGarde’s Sunjammer solar sail. Sunjammer will test key solar sail technologies as well as deliver the Solar Wind Analyzer (SWAN) and the MAGIC Magnetometer to the L1 Earth-Sun Lagrange point. Sunjammer will launch on a Falcon-9 rocket and deploy a 1200 square metre solar sail weighing only 32 kilograms. This will be a great one for ground satellite-spotters to track as well as it heads out!

Gaia Opens for Business: Launched on a brilliant night-shot out of the Kourou Space Center in French Guiana on December 19th of last year, the European Space Agency’s Gaia space observatory will begin its astrometry mission in 2014, creating most accurate map yet constructed of our Milky Way Galaxy. But we also anticipate exciting new discoveries due to spin-offs from this mission, to include the discovery of new exoplanets, asteroids, comets and much more.

And as in years previous, the quest to explore brave new worlds will be done against the backdrop of tightening budgets. Just like in household budgets, modern spaceflight is a continual conflict between what we would wish and what we can afford. In recent years, no mission seems to be safe, and there have even been occasional congressional rumblings to pull the plug on missions already underway. Interesting times, indeed… 2014 promises to be an extraordinary time in spaceflight and space science, both on Earth and beyond.