Hydraotes Chaos is a typical example of ‘chaotic terrain.’ This large basin lies in the Martian highlands, near the equator. Credit: ESA.
This isn’t quite like Luke’s trench run in the Battle of Yavin, but it’s waaay more awesome in that this is real.
Go grab your red–green or red–blue 3-D glasses (you always have a pair right by your desk, right?) and enjoy this great flyover video from ESA showcasing some very interesting landforms on Mars that planetary geologists refer to as ‘chaotic terrain.’ There’s nothing quite like this on Earth, and scattered throughout a large area to both the west and east of Valles Marineris are hundreds of isolated mountains up to 2,000 meters high. “Seen from orbit, they form a bizarre, chaotic pattern,” say scientists from the Mars Express orbiter.
What created this weird landscape? Scientists think that during Mars’ early history, water in the form of ice was stored in cavities beneath the surface of the highlands; this was then heated and thawed out. It was then placed under so much pressure that it escaped to the surface with great force through fissures and fault zones. As it flowed out, the water eroded the terrain and gradually left behind the striking landscape visible today. Another factor supporting this theory is that many of the chaotic terrains on Mars are located at the head of large outflow channels, through which enormous quantities of water flowed out of the highlands towards the northern lowlands.
The data used to generate the images and the simulated flyover were acquired with the High Resolution Stereo Camera on ESA’s Mars Express orbiter.
Is this an image of Comet Siding Spring? It's the only fuzzy object in the field photographed on Sol 3817 (October 19) by the Opportunity Rover. Click for original raw image.
It looks like NASA’s hard-working Opportunity Rover nabbed our very first pictures of a comet seen from another world! A study of raw images taken by the rover turned up a very promising fuzzy object. Only three night sky pictures were posted today, but two clearly show a fuzzy spot near the center of the field. Stars show as points of light and there are what appear to be a smattering of cosmic ray hits, but in the photo above, the brightest object is slightly elongated (trailed during the exposure?) and cometary in appearance.
Here’s another photo:
A second picture from Opportunity possibly showing the comet. Click for original. Credit: NASA/JPL-Caltech
Looking back over earlier photos of the sky taken on Sol 3212 show only stars and no fuzzy blobs. The pictures were taken around 4:13 a.m. local time with the Sun 25 degrees below the horizon. Opportunity can photograph diffuse objects as dim as the Andromeda Galaxy at magnitude +3.5 and stars down to magnitude +6 or +7. That’s similar to what we see on Earth on very dark night. Since the comet glowed far brighter at around magnitude -5 by some estimates, it would be a relatively easy catch for the rover panoramic camera.
Curiousity Navcam photo of the sky on October 19, 2014, shows the silhouetted rim of Gale Crater and lots of noise. Credit: NASA/JPL-Caltech
NASA has also posted images taken by the Curiosity Rover but for the life of me I can’t find any sign of the Comet Siding Spring. Maybe it’ll pop out after the noise is removed. We’ll keep you posted.
Another Curiosity photo of the sky. If you look closely you’ll see stars among the noise. Click for original Credit: NASA/JPL-Caltech
Comet Siding Spring approaches within a degree of Mars at 5:07 a.m. CDT today October 19. Closest approach happens around 1:28 p.m. CDT (18:28 UT) when the comet will brush about 83,240 miles from the planet's surface. Image copyright SEN / Damian Peach
Astrophotographer Damian Peach shares this spectacular image of comet C/2013 A1 Siding Spring approaching Mars taken just hours ago. The faint comet shows a small, condensed coma and bent tail against the glaring orange glow of the brilliant planet. Most photos of comets passing by a planet or deep sky object are lucky line-of-sight pairings with the comet in the foreground and object light years away in the background. Not this one. Both Siding Spring and Mars lie at nearly the identical distance from Earth of 151 million miles (243 million km).
Artist view of the comet passing closest to Mars this afternoon October 19. At the time, the Mars orbiters from the U.S., Europe and India will be huddled on the opposite side of the planet to avoid possible impacts from comet dust. Credit: NASA
When closest to Mars this afternoon, Siding Spring is expected to shine at around magnitude -5 or about twice as bright as Venus. Mind you, that estimate considers the entire comet crunched down into a dot. But for those who remember, Comet Hale-Bopp remained at zero magnitude, 100 times fainter than Siding Spring, and made for one of the most impressive naked eye sights on spring evenings in 1997.
More recently, Comet McNaught climaxed at magnitude -5 in the daytime sky near the Sun in January 2007. It was plainly visible in binoculars and telescopes in a blue sky if you knew exactly where to look and took care to avoid the Sun. Would-be Martians are far more fortunate, with Siding Spring appearing high overhead in a dark sky from some locations, including that of NASA’s Curiosity Rover.
Comet C/2013 Siding Spring as it rises and sets over the Curiosity Rover this weekend October 18-19. Credit: Solarsystemscope.com
Right on time for today’s encounter, the folks at Solarsystemscope.com have rolled out an interactive simulation of Comet Siding Spring’s appearance in the sky above Curiosity. Just click the play button on the control panel above to run it live. Seen from Mars, the comet bobs along Eridanus the River southwest of Orion, passing high in the southern sky overnight. What a sight!
Another photo, just in, taken of the comet and Mars today by Rolando Ligustri. Beautiful!
The comet nucleus is only about 0.4 miles (700 meters) across, but the coma or atmosphere fluffs out to around 12,000 miles (19,300 km). Seen from the ground, Siding Spring would span about 8°of sky or 16 full Moons from head to tail. Moving at 1.5° per minute, we could watch crawl across the heavens in real time with the naked eye. Wish I zoom to Mars for a look, but the rovers and orbiters will be our eyes as they study and photograph the comet during its brief flyby. As soon as those pictures become available, we’ll publish them here. Can’t wait!
Come Siding Spring comes out the other side!
While we’re waiting, amateur astronomers have been busy shooting additional photos and creating videos from their images. Fritz Helmut Hemmerich made this video from 1200-meters at Tenerife in the Canary Islands showing Comet Siding Spring immediately after its Mars encounter. One thing we know for certain is that the comet is intact after its close brush.
Negative image showing Comet Siding Spring closely approaching Mars today. Credit: Peter Lake
And find our more amazing photos and information at Sen TV, and you can follow them on Twitter at @sen.
Comet C/2013 A1 Siding Spring passed between the Small Magellanic Cloud (left) and the rich globular cluster NGC 130 on August 29, 2014. Credit: Rolando Ligustri
We present here a compendium of Universe Today articles on comet Siding Spring. Altogether 18 Universe Today stories and counting have represented our on-going coverage of a once in a lifetime event. The articles beginning in February 2013, just days after its discovery, lead to the comet’s penultimate event – the flyby of Mars, October 19, 2014. While comet Siding Spring will reach perihelion just 6 days later, October 25, 2014, it will hardly have sensed the true power and impact that our Sun can have on a comet.
Siding Spring’s Oort Cloud cousin, Comet ISON in November 2013 encountered the Sun at a mere 1.86 million km. The intensity of the Sun’s glare was 12,600 times greater than what Siding Spring will experience in a few days. Comet ISON did not survive its passage around the Sun but Comet Siding Spring will soon turn back and begin a very long journey to its place of origin, the Oort Cloud far beyond Pluto.
An animation of comet Siding Springs passage through the inner Solar System. The scale size of its place of origin would dwarf the orbits of the Solar System to little more than a small dot. (Illustration Credit: Near-Earth Object (NEO) office, NASA/JPL)
The closest approach for comet Siding Spring with the Sun – perihelion is at a distance of 1.39875 Astronomical Units (1 AU being the distance between the Earth and Sun), still 209 million km (130 million miles). The exact period of the comet is not exactly known but it is measured in millions of years. In my childhood astronomy book, it stated that comet Halley, when it is at its furthest distance from the Sun, is moving no faster than a galloping horse. This has also been all that comet Siding Spring could muster for millions of years – the slightest of movement in the direction of the Sun.
It is only in the last 3 years, out all the millions spent on its journey, that it has felt the heat of the Sun and been in proximity to the planetary bodies of our Solar System. This is story of all long period comets. A video camera on Siding Spring would have recorded the emergence and evolution of one primate out of several, one that left the trees to stand on two legs, whose brain grew in size and complexity and has achieved all the technological wonders (and horrors) we know of today.
Now with its close encounter with Mars, the planet’s gravity will bend the trajectory of the comet and reduce its orbital period to approximately one million years. No one will be waiting up late for its next return to the inner Solar System.
It is also unknown what force in the depths of the Oort cloud nudged the comet into its encounter with Mars and the Sun. Like the millions of other Oort cloud objects, Siding Spring has spent its existence – 4.5 Billion years, in the darkness of deep space, with its parent star, the Sun, nothing more than a point of light, the brightest star in its sky. The gravitational force that nudged it may have been a passing star, another cometary body or possibly a larger trans-Neptunian object the size of Pluto and even as large as Mars or the Earth.
The forces of nature on Earth cause a constant turning over geological features. Our oceans and atmosphere are constantly recycling water and gases. The comets that we receive from the Oort Cloud are objects as old as our Solar System. Yet it is the close encounter with Mars that has raised the specter of an otherwise small ordinary comet. All these comets from deep space are fascinating gems nearly unaltered for 1/3rd of the time span of the known Universe.
Comet 2013 A1 Siding Spring on October 17, 2014, with two days to go until its Martian encounter. Very dense Milkyway starfield in the background with many darker obscured regions. Credit and copyright: Damian Peach.
The excitement continues to build as Comet Siding Spring rapidly approaches the Red Planet, and here’s the latest view of the comet from prolific astrophotographer Damian Peach. While Comet Siding Spring’s encounter with Mars on October 19 will not be visible from Earth with the unaided eye, skywatchers in mid-northern latitudes, can now view the comet; an 8-inch (20 cm) or larger telescopes is needed to follow the comet as it travels from Scorpius north to Ophiuchus and its encounter with Mars on October 19.
The comet will come within 139,500 km (86,000 miles) above the planet’s surface on Sunday.
As our David Dickinson discussed earlier this week, if you were an astronaut stranded on the surface of Mars, the comet’s passage would be a spectacular sight under the dark Martian sky. Some scientists suggest it could even spawn a short but brilliant meteor shower caused by cometary dust grains plunging into the Martian atmosphere.
The spacecraft in orbit around Mars will be watching Comet Siding Spring too. The fleet of spacecraft from ESA, NASA and ISRO will hide behind the Red Planet on Sunday morning, trying to avoid possible bombardment by tiny grains of dust from the comet. But before and after that, the spacecraft will attempt to gather data on the comet as well as try to measure how the gas and dust interact with the Martian atmosphere.
Stay tuned for news on the comet’s encounter with Mars.
Three views of an escaping atmosphere, obtained by MAVEN’s Imaging Ultraviolet Spectrograph. By observing all of the products of water and carbon dioxide breakdown, MAVEN's remote sensing team can characterize the processes that drive atmospheric loss on Mars.
Image Credit:
University of Colorado/NASA
It’s been less than a month since NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft slipped into orbit. But it’s already provided mission scientists their first look at Mars’ tenuous atmosphere.
“Everything is performing well so far,” said Bruce Jakosky, the mission’s principle investigator, in a news release. “All the instruments are showing data quality that is better than anticipated at this early stage of the mission. The spacecraft is performing beautifully. It’s turning out to be an easy and straightforward spacecraft to fly, at least so far. It really looks as if we’re headed for an exciting science mission.”
Data collected by MAVEN will answer a longstanding puzzle among planetary scientists. There’s ample evidence that early in the Red Planet’s history it had a much denser atmosphere. Rain fell from the sky and water carved its surface. But then the atmosphere vanished, and scientists are unsure why.
One leading theory is that the gas escaped to space, stripped away by the solar wind rushing past. (Click here to see a cool animation of that process.) Here on Earth, our magnetosphere helps protect our atmosphere from the solar wind. But once Mars lost its own magnetosphere, billions of years ago, its atmosphere became vulnerable.
MAVEN’s spectrometers will attempt to determine if hydrogen atoms, torn from water molecules by ultraviolet sunlight, are escaping to space and at what rate. Already, the spacecraft has observed the edges of the Martian atmosphere using its Imaging Ultraviolet Spectrograph (IUVS) camera, which is sensitive to the sunlight reflected by the atoms.
“With these observations, MAVEN’s IUVS has obtained the most complete picture of the extended Martian upper atmosphere ever made,” said team member Mike Chaffin from Colorado University at Boulder.
So far scientists have used IUVS to create a map of Mars’ ozone. “With these maps we have the kind of complete and simultaneous coverage of Mars that is usually only possible for Earth,” said team member Justin Deighan, also from CU-Boulder.
There will be about two weeks of additional instrument calibration and testing before MAVEN starts its primary science mission in early to mid-November. It will then likely take a few additional months to build up enough measurements to have a clear sense of what’s going on. But the initial results are promising.
Artist's conception of Mars One human settlement. Credit: Mars One/Brian Versteeg
How possible is it to land humans on Mars? And can Mars One, the organization proposing to start with sending four astronauts one way, capable of doing it by 2025 as it promises?
A new study says that the Mars One concept could fail on several points: oxygen levels could skyrocket unsafely. Using the local resources to generate habitability is unproven. The technology is expensive. But the founder of Mars One says the Massachusetts Institute of Technology (MIT) student study is based on the wrong assumptions.
“It’s based on technology available on the ISS [International Space Station],” said Bas Landorp in an interview with Universe Today. “So you end up with a completely different Mars mission than Mars One. So their analysis has nothing to do with our mission.”
The mission has sparked a debate about sending humans on a trip with no promise for a return, but thousands of applicants vied for the chance to do it. After two cuts, the interim shortlist is now at 700 people. Those folks are awaiting interviews (more news is coming shortly, Landorp says) and no date has yet been announced for the next “cut.”
ISRO’s Mars Orbiter Mission captures spectacular portrait of the Red Planet and swirling dust storms with the on-board Mars Color Camera from an altitude of 74500 km on Sept. 28, 2014. Credit: ISRO
A couple of weeks ago, MIT students presented a technical feasibility analysis of Mars One at the International Astronautical Congress in Toronto, Canada. The study is 35 pages long, so we recommend you read it to get the whole picture. The students’ main concerns are that crops (if they are responsible for 100% of the food) would send oxygen levels to unsafe margins, with no way to remove it. There are concerns with how well the in-situ resource utilization (using the resources on Mars to live off of) would perform. And the mission would cost $4.5 billion at a minimum — for the first crew only.
Cost: To get to Mars, the students say it will cost $4.5 billion and take 15 Falcon Heavy launches (a proposed next-generation rocket from SpaceX). Landorp says he can do it for $1.625 billion (since he doesn’t require constant Earth resupply) and as few as 13 launches (assuming $125 million per launch, a figure Landrop says is from SpaceX) by taking advantage of a few quirks of physics. If Mars One chooses a landing site that is four kilometers (2.5 miles) below the average Martian surface height, they will have both a thicker atmosphere and more time to land the payloads than, say, the Curiosity rover that landed about two kilometers (1.24 miles) above the average surface height. Mars One’s numbers show they could carry a payload of 2,500 kilograms (5,512 pounds) per mission, which they say is well within reach of what spacecraft can do today. The 13 launches would be divided into 11 robotic launches to send equipment to the surface, and two for humans (one to head to Earth orbit for assembly, and the other for the colonists to head to the in-orbit spacecraft and fly to Mars. The assembly crew would then fly back to Earth on the launch vehicle.)
Life support: While many of the technologies planned for use in life support are similar to those on the ISS — such as a trace gas system for air revitalization — Landorp says there will be some crucial differences. They are in talks with Paragon Space Systems Corp. (which describes itself as an environmental control firm for extreme environments, and whose customers include NASA and Bigelow.) As for the unsafe oxygen levels, Landorp points out there are plenty of oxygen removal systems available and that are used in hospitals and militaries. All that is needed is more testing in space. Landorp also points out these systems will be tested for two years robotically before humans land. “If that is not successful, then obviously we will not send humans,” he said.
The proposed Falcon Heavy rocket. Credit: SpaceX
In-situ resource utilization: Landorp acknowledges this requires more study, but says the robotic missions will be an important precursor for the human landings. Technologies needing to be developed will include nitrogen extraction from the Martian atmosphere. Oxygen production from water is well-studied in space, but water from the Martian surface (through vaporizing water in the soil) will require more work.
Another concern raised in media from time to time is where the money is coming from to fund Mars One. Landorp says right now funds are flowing from private investors. Mars One representatives are also in serious talks with a United Kingdom-based listed investment fund willing to finance the mission. In the long run, Landorp is confident money will come from broadcast deals similar to what partially fund the Olympics and the Fédération Internationale de Football Association (FIFA) competitions. Associated sponsorships would also help. But these won’t kick in until the colonists launch and land, since that’s when the world’s eyeballs will be on the mission.
Another stream of revenue, which may take five to seven years to kick in, will be intellectual property deals Mars One one representatives are working on closing now with potential suppliers, such as Lockheed Martin and Paragon. These agreements, should they go through as planned, would give Mars One a share of future revenue from any technologies flowing from the IP. “In the short term it’s not that interesting, it takes time to mature, but in the long term that will be interesting,” Landorp said.
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.
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.
The Lunar Reconnaissance Orbiter turned for a quick look at Earth and one of our closest planetary neighbors—Mars. Credit: NASA/GSFC/Arizona State University,
Wow, this doesn’t happen very often: Earth and Mars together in one photo. To make the image even more unique, it was taken from lunar orbit by the Lunar Reconnaissance Orbiter. This two-for-one photo was was acquired in a single shot on May 24, 2014, by the Narrow Angle Camera (NAC) on LRO as the spacecraft was turned to face the Earth, instead of its usual view of looking down at the Moon.
The LRO imaging team said seeing the planets together in one image makes the two worlds seem not so far apart, and that the Moon still might have a role to play in future exploration.
“The juxtaposition of Earth and Mars seen from the Moon is a poignant reminder that the Moon would make a convenient waypoint for explorers bound for the fourth planet and beyond!” said the LRO team on their website. “In the near-future, the Moon could serve as a test-bed for construction and resource utilization technologies. Longer-range plans may include the Moon as a resource depot or base of operations for interplanetary activities.”
Watch a video created from this image where it appears you are flying from the Earth to Mars:
The LROC team said this imaging sequence required a significant amount of planning, and that prior to the “conjunction” event, they took practice images of Mars to refine the timing and camera settings.
When the spacecraft captured this image, Earth was about 376,687 kilometers (234,062 miles) away from LRO and Mars was 112.5 million kilometers away. So, Mars was about 300 times farther from the Moon than the Earth.
The NAC is actually two cameras, and each NAC image is built from rows of pixels acquired one after another, and then the left and right images are stitched together to make a complete NAC pair. “If the spacecraft was not moving, the rows of pixels would image the same area over and over; it is the spacecraft motion, combined with fine-tuning of the camera exposure time, that enables the final image, such as this Earth-Mars view,” the LRO team explained.
Check out more about this image on the LRO website, which includes a zoomable, interactive version of the photo.
Comet C/2013 A1 Siding Spring passes just north of the sparking Butterfly Cluster on October 9. Credit: Rolando Ligustri
With excitement building as Comet Siding Spring rapidly approaches the Red Planet, we’ll soon have the opportunity to spot it through our own telescopes. Dark skies return this week with the moon now past full and rising later each night. Until recently, the comet could only be seen by skywatchers living in southern latitudes. Now it’s popped high enough above the southern horizon to see from mid-northern latitudes, albeit low in the sky. Observers with 8-inch (20 cm) or larger telescopes can follow the comet as it travels from Scorpius north to Ophiuchus and its encounter with Mars on October 19.
JPL Horizons light curve for Comet C/2013 A1 Siding Spring shows it brightening as it approaches Earth and then fading after late September. For our purposes we’re interested in the purple squares which are visual magnitude estimates of the whole comet submitted to the Comet Observation Database. Recently, the comet has faded faster than predictions. Click for more details. Credit: CIOC
Until late September, the comet had been brightening as forecast based on the simple principle that the closer an object is to Earth the brighter it appears in the sky. Siding Spring came just shy of 1 A.U. of Earth in early September and has since been slip-sliding away. All through the first weeks of September it glowed at magnitude +9-10 and could be spotted in small telescopes trekking across the south polar constellations. Now on the cusp of its big moment with Mars, Siding Spring has been fading faster than expected.
It could be running low on exposed ice or concluding a long, slow outburst. Maybe it’s as simple as our changing perspective on the comet’s tail – we see it from the side now instead of looking down the tail where reflective dust piles up along our line of sight. No one knows exactly why, but given that comets are famous for their unpredictability due to their fragile nature and the varying rates at which they sputter away ice and dust, we shouldn’t be too surprised.
The paths of Mars and Comet Siding Spring are clearly on a (near) collision course! Watch over the coming nights as they draw ever closer. This map shows the sky facing southwest at nightfall from Kansas City, Missouri. From the central U.S. the comet will be about 13-15º high but only ~5-8º altitude in the northern border states. Source: Chris Marriott’s SkyMap
So what does that mean for observers? The most recent observations put the comet at about magnitude +11 with a loosely condensed coma and diameter of about one arc minute or a little larger than Jupiter appears in a telescope. It’s a small, relatively faint object now but should be visible in 8-inch and larger telescopes from a dark sky assuming it doesn’t “drop off the deep end” and fade even faster. With Mars nearby, finding the general location of Siding Spring is easy. The maps will help you pinpoint it.
Daily positions of Comet Siding Spring October 10-20 from the central U.S. at nightfall. Stars shown to magnitude +11.5. Closest approach to Mars is October 19. The brighter stars 3 Sagittarii, 44 and 51 Ophiuchi and Theta Ophiuchi are labeled. Click for large version to print and use at the telescope. Source: Chris Marriott’s SkyMap
The good news is that the comet is heading straight north and getting higher in the sky every night. The bad news is that it’s also dropping westward each evening mostly negating its northerly altitude gains. Those in the southern U.S. will have the best viewing window with Siding Spring 20º high at nightfall (14º in the central states and 6º in the north). To ensure success, find a spot with a wide open view as far down to the southwestern horizon as possible. You’ll make best use of your time and see the comet highest if you set up during evening twilight and begin searching as soon as the sky is dark. Given that Mars is 1st magnitude and the comet has faded more than expected, it may be difficult to see against the planet’s glare on the 19th. Not that I want to dissuade you from trying, but the nights leading up to and after the encounter will prove better for comet spotting.
Need to get in closer? This more detailed map shows Mars and Comet Siding Spring nightly October 15-20 with stars to magnitude +12. Time and location are the same as the map above. Click for larger version. Source: Chris Marriott’s SkyMap
The fluffball passed the glittery Butterfly Cluster (M6) in Scorpius on October 9 displaying an attractive curved tail pointing southeast. Tim Reyes of Universe Today calculated the current tail length at ~621,000 miles (1 million km) with a coma ~19,900 miles across (32,000 km). Closest approach occurs around 1:28 p.m. Central Daylight Time (18:28 UT) October 19 when the comet will miss Mars by only 88,000 miles (141,600 km). Dust particles leaving the coma will rip by the planet at ~125,000 mph (56 km/sec). Will they pass close enough to set the Martian sky a-sparkle with meteors?
Not only will the Mars orbiters gather information about the comet and its dust before, during and after the encounter, a fleet of additional telescopes will make the most of the rare opportunity. Credit: NASA
According to a recent NASA press release, the period of greatest risk to orbiting spacecraft will start about 90 minutes after the closest approach of the comet’s nucleus and will last about 20 minutes, when Mars will come closest to the center of the widening trail of dust flying from the comet’s nucleus. Since the comet will barely graze the planet, dust impacts on orbiting spacecraft may or may not happen.
Back on Earth we can watch the daredevil pass by telescope or catch it live on the Web here:
