Oval impact craters north of Olympus Mons (NASA)

Could Strange Mars Craters be from a Fallen Third Moon?

24 Oct , 2008 by

[/caption]Was there a third Martian moon orbiting the planet? Did Phobos and Deimos have a triplet sibling? According to the discovery of two elliptical impact craters, there might just have been another moon, but it ploughed into the Red Planet’s surface a long time ago. The moonlet would have been approximately 1.5 km wide (0.9 miles), and it will have succumbed to the Mars gravity, entering the atmosphere at a shallow angle. As it tumbled through the atmosphere it broke in two, hitting the surface and creating two elongated impact craters, near-perfectly aligned.

It is thought that the “third moon” of Mars dropped from orbit a billion years ago and the same will happen with Phobos in a few million years. However, there might be another explanation, with no third moonlet in sight…

Observations of the Martian surface, just north of Olympus Mons, show two oval-shaped craters (pictured top). Usually impact craters are approximately circular, so the elongated craters indicate the impactor(s) entered the atmosphere at a very shallow angle. This isn’t the only strange characteristic of these two craters. They lie 12.5 km (7.8 miles) apart and they are almost exactly aligned from east to west (they are off-alignment by only 3.48&degwink. The larger crater is 10 km (6.2 miles) wide at its longest point, and the smaller crater is 3km (1.9 miles) wide.

There are two possible answers to this puzzle, but researchers are having a hard time in agreeing on which one. In a recent publication, John Chappelow and Rob Herrick of the University of Alaska, Fairbanks, have calculated that the impact craters were caused by a small moon that entered the atmosphere, broke into two (due to atmospheric drag) and then struck the surface at an oblique angle of 10° or less. The moonlet would have been 1.5 km (0.9 miles) in diameter. This sounds feasible, after all for both craters to be aligned, one would think they came from the same mass, right?

NASAs Lunar Orbiter spacecraft imaged the Messier A (right) and B craters on the Moon. Messier A is about 11 km long (NASA)

The lunar Messier craters (NASA)

This moon-impact theory has a few drawbacks however. The first problem is that the impact craters are located at 40° latitude in Mars’ northern hemisphere. One would expect natural satellites to orbit around the equatorial plane if their orbits are stable (hovering around 0° latitude). “Any close natural satellite must, like Phobos, orbit in Mars’s equatorial plane,” said Jay Melosh, a crater expert at the University of Arizona in Tucson, who is highly sceptical of Chappelow and Herrick’s findings.

However, Herrick believes that the moonlet may not have established a stable orbit, above the equator. “We don’t know the details of the [moonlet’s] capture mechanism, so I don’t know that we can definitively say that the object must have moved to an equatorial orbit before spiralling in,” countered Herrick.

Artist impression of binary asteroid 90 Antiope (ESO)

Artist impression of binary asteroid 90 Antiope (ESO)

Melosh argues that the craters may have been caused by a binary asteroid (or “double asteroids”) entering the Martian atmosphere at a very shallow angle. After all, there is a confirmed example of a binary asteroid impact on the Moon (a.k.a. the Messier craters on the Moon, pictured above). Chappelow however disputed this claim saying, “In such a case, the craters should be oriented randomly.” After all, wouldn’t the binary asteroid have a randomly oriented orbital plane?

Apparently not. It appears that over hundreds of thousands of years of asteroid evolution, the effect of sunlight has a huge role to play in the dynamics of binary asteroid formation. A process known as the “Yarkovsky-O’Keefe-Radzievskii-Paddack Effect,” or the YORP Effect, causes the uneven heating of an asteroid. Carrying a tiny jolt of momentum, photons are emitted from the surface in jets, eventually causing the asteroid to spin. Eventually a piece of rock breaks loose, forming the binary asteroid. It would appear there is an observed trend for the majority of binary asteroids to orbit in the same plane as the rest of the Solar System.

So it seems possible that a binary asteroid could create the two elongated and aligned impact craters after all.

Regardless, whether a third moon or binary asteroid hit Mars, it will be of little comfort to Phobos. The moon (with a mean radius of 11 km) is slowly dropping in altitude due to tidal forces. In about 11 million years it will either crash into Mars or be ripped apart through gravitational shear. Either way, Phobos is a doomed moon.

Original Source: Space.com


Sort by:   newest | oldest | most voted
quantum_flux
Member
October 24, 2008 6:47 PM

Phobos isn’t necessarily doomed. Who knows what a future lunar colony might do to eliminate the impact of phobos (scotch tape anyone?).

Jorge
Guest
October 24, 2008 4:32 PM

Isn’t a third explanation possible?

That a single asteroid entered Mars’ atmosphere at a shallow angle, broke up just before hitting the ground and then slammed in?

Sort of a mix of the two presented above.

fixwhatyoubroke
Guest
fixwhatyoubroke
October 24, 2008 5:33 PM

link….wink

marcellus
Guest
marcellus
October 25, 2008 12:56 AM

Very cool article. More, please.

Neil Marsh
Member
Neil Marsh
October 25, 2008 1:41 AM

Back when I was entranced by the 1st Mars surface fotos, I collected some shots of interest, but alas have lost the planetary references … but the large “gouge” shown in the attached is similar to the little ones in this article; & judging by the color markings, has already been well-studied. Hope the shot turns out!
>>>>>>>>>>>>>>Sorry, it didn’t! Someone tell me how to send a gif file??

Maxwell
Member
Maxwell
October 24, 2008 7:44 PM

If human activity could affect the orbits of heavy objects around mars (or in the asteroid belt for that matter) colonists may actually be interested in hitting their world with big rocks.

Rocks of specific materials anyway. As a cheap way to deliver a substance in bulk with just a gravity tug and some patience…
Its not like you can harm the martian environment by dropping stuff on it.

mewo
Member
mewo
October 24, 2008 8:36 PM

The best way of getting greenhouse gases like CO2 and water vapour into Mars’s atmosphere might be to drop a big rock onto the polar ice cap.

mars_stu
Member
October 25, 2008 12:18 AM

I think Ann Clayborne might have something to say about *that*… wink

Pauli
Guest
Pauli
October 25, 2008 6:33 AM

While terra-forming the planet would be nice, would the atmosphere stay on the planet? I think I read somewhere that due to the weak magnetic field of the planet, solar wind has blown off most of the atmosphere Mars had. I wonder if that dropped down moon had anything to do with weakening the magnetosphere..

Anyway, wouldn’t the dropping Phobos would be a slight concern for the future colonies on Mars, I know it’s millions of years ahead, but still. I guess they should have something figured out by then, as long as it’s not too late to act.

Wesley
Guest
Wesley
October 25, 2008 8:30 AM

I think Chappelow was correct. Even given the YORP effect, the surface jets won’t necessarily form in a spot aligned with the plane of the asteroid’s orbit. They would naturally form where the asteroid’s composition is suitable to generate them.

Maxwell
Member
Maxwell
October 25, 2008 9:00 AM

I think the real questions are how fast can we build an atmosphere there and how long can Mars retain one. The planet is not that small and the solar winds don’t appear to be that strong.

If we can do things to terraform the place in 1,000 years and the changes only last 1,000,000 years… well thats not really a problem, is it?

Jorge
Guest
October 25, 2008 9:17 AM
I’m with maxwell on this one. Even the Moon could eventually be terraformed for a while, if we’d be able to build an atmosphere there quickly enough. Mars has several advantages: it’s larger, hence heavier, hence with larger g force, and it’s colder, hence the average kinetic energy of air molecules would be lower, which means they’d need to receive more energy to escape (even considering that to be really terraformed, it’d have to be warmed up quite a bit). Not to mention much shorter days. Still, it’s not that easy. It’s not as if Mars were a liophilised (spelling?) Earth, just waiting for water to be added. Any planet is a very complex system, and we just… Read more »
IBY
Guest
October 25, 2008 10:58 AM

Is Phobos the one with the huge creater on top? If so, nooooooo! because that is my favorite Martian moon. smile

Luke
Guest
Luke
October 25, 2008 11:42 AM

How about Martians building two nuclear reactors that exploded leaving only 2 huge craters behind. This would also be the cause of the death of the Martian race.

Blondin
Guest
Blondin
October 25, 2008 2:56 PM

I read a SciFi story once about a third moon orbiting Mars even closer than Phobos. A character in the story named it “Bottomos”.

I believe the story was called “The Holes Around Mars” but I can’t remember who the author was.

BHC
Guest
October 27, 2008 11:24 AM

Google is your friend… found this

Bottomos
“My favorite form within the sci-fi genre is the short story, and one especially cute little tale that stuck in my head is about Mars. I read “The Holes Around Mars” by (Jerome) Bixby in an anthology, although it was most likely first published in a magazine.

at link in the website part of this post.

Huygens
Guest
Huygens
October 27, 2008 12:38 PM

Phobos and Deimos will be utilized long before they go anywhere in regards to Mars, assuming we live long enough.

Then of course Mars itself will be used for making the Dyson Shell.

ancelmo
Guest
ancelmo
November 5, 2008 4:33 AM
VIERTE THEORIE VON ASTRONOMIE GRACELIANA. Autor – Ancelmo Graceli Luiz. Brasilianer, Professor, theoretischer Forscher, abgestufte Philosophie. THEORIE VON ASTRONOMIE der PROPORTIONATITÄT DER BAHNEN für die UMDREHUNG und die ÄQUATORIALE GESCHWINDIGKEIT. E UNREGELMÄSSIGKEITEN VON BAHNEN Und VON UMDREHUNG Für Den ENERGIE-ZERFALL. VOM FAST NICHTS KANN ALLES – AUSGENOMMEN GOTT ERSCHEINEN. FOLGLICH ist er DAS NUR ABSOLUTE. Referenzen. Die Arbeit wird mit ergägenzt. Theorie 1-A des estruturante fluxonário Universum und cosmofísica graceliana. 2-Teoria von graceliana Astronomie von energeticidade und von MASER. 3-Teoria von alternancidade Astronomie und Abweichung. 4-Teoria von Astronomie des Ursprung, der Umdrehung, des Abbaus und der Weiterentwicklung. 5-Teoria von Astronomie von fisicidade, von Zerfall und von Wiedereingliederung. Allgemeines 6-Teoria für Astronomie und cosmo. 7-Teoria der Mikrophysik und der… Read more »
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