Russia’s Second Shot at Phobos May Return Bits of Mars As Well

After the tragic failure of the first Phobos-Grunt mission to even make it out of low-Earth orbit, the Russian space agency (Roscosmos) is hoping to give it another go at Mars’ largest moon with the Phobos-Grunt 2 mission in 2020. This new-and-improved version of the spacecraft will also feature a lander and return stage, and, if successful, may not only end up sending back pieces of Phobos but of Mars as well.

The origins of Phobos have long been a topic of planetary science debate. Did it form with Mars as a planet? Is it a wayward asteroid that ventured too closely to Mars? Or is it a chunk of the Red Planet blasted up into orbit from an ancient impact event? Only in-depth examination of its surface material will allow scientists to determine which scenario is most likely (or if the correct answer is really “none of the above”) and Russia’s ambitious Phobos-Grunt mission attempted to become the first ever to not only land on the 16-mile-wide moon but also send samples back to Earth.

Unfortunately it wasn’t in the cards. After launching on Nov. 9, 2011, Phobos-Grunt’s upper stage failed to ignite, stranding it in low-Earth orbit. After all attempts to re-establish communication and control of the ill-fated spacecraft failed, Phobos-Grunt crashed back to Earth on Jan. 15, impacting in the southern Pacific off the coast of Chile.

But with a decade of development already invested in the mission, Roscosmos is willing to try again. “Ad astra per aspera,” as it’s said, and Phobos-Grunt 2 will attempt to overcome all hardships in 2020 to do what its predecessor couldn’t.

Read more: Russia to Try Again for Phobos-Grunt?

And, according to participating researchers James Head and Kenneth Ramsley from Brown University in Providence, Rhode Island, the sample mission could end up being a “twofer.”

Phobos floats in front of Mars' horizon in a Mars Express image from January 2007 (ESA)
Phobos floats in front of Mars’ horizon in a Mars Express image from January 2007 (ESA)

Orbiting at an altitude of only 5,840 miles (9,400 km) Phobos has been passing through plumes material periodically blown off of Mars by impact events. Its surface soil very likely contains a good amount of Mars itself, scooped up over the millennia.

“When an impactor hits Mars, only a certain of proportion of ejecta will have enough velocity to reach the altitude of Phobos, and Phobos’ orbital path intersects only a certain proportion of that,” said Ramsley, a visiting researcher in Brown’s planetary geosciences group. “So we can crunch those numbers and find out what proportion of material on the surface of Phobos comes from Mars.”

Determining that ratio would then help figure out where Phobos was in Mars orbit millions of years ago, which in turn could point at its origins.

“Only recently — in the last several 100 million years or so — has Phobos orbited so close to Mars,”  Ramsley said. “In the distant past it orbited much higher up. So that’s why you’re going to see probably 10 to 100 times higher concentration in the upper regolith as opposed to deeper down.”

In addition, having an actual sample of Phobos (along with stowaway bits of Mars) in hand on Earth, as well as all the data acquired during the mission itself, would give scientists invaluable insight to the moon’s as-yet-unknown internal composition.

“Phobos has really low density,” said Head, professor of geological sciences at Brown and an author on the study. “Is that low density due to ice in its interior or is it due to Phobos being completely fragmented, like a loose rubble pile? We don’t know.”

The study was published in Volume 87 of Space and Planetary Science (Mars impact ejecta in the regolith of Phobos: Bulk concentration and distribution.)

Source: Brown University news release and

See more images of Phobos here.

12 Replies to “Russia’s Second Shot at Phobos May Return Bits of Mars As Well”

  1. Why is there a return sampler mission for a moon of mars, and not mars? Is it that much easier to reach escape veloicity with a sample from that moon than it is from mars? I dont know what the gravity differences are like on each place.
    Does pride have any factor here, with previous failed attempts making it a target to regain face?

    Either way it’s an exciting mission, and I am looking forward to what it brings.

    1. Right on. Thanks for the detailed replies. It makes sense now. That comic linked by Gopher was very helpful too, puts it all into perspective.

  2. Phobos is only around sixteen km wide, and it has a very low density. With those factors its gravity is practically nonexistant, if you were standing on the surface you could throw a baseball and reach escape velocity without too much effort.

  3. Good question!

    Mars has 1/3 of Earth’s surface gravity. You need a decent sized rocket to get off the surface. You’d have to haul that rocket all the way from Earth, then find a way to land it. The cost of such a mission would be phenomenally high (5 to 10 billion most likely).

    Phobos and it’s brother moon Deimos are tiny. As Randall Munroe points out in the fantastic and educational comic that I’ve linked to at the bottom of this post (and as Dav_Daddy points as well), you could throw a baseball hard enough on Phobos to send it into orbit. On Deimos you could ride a bike off a ramp and jump into orbit yourself. Because of their tiny mass a probe can escape from either moon using only tiny control thrusters. There is no need for a separate rocket at all.

    Linky to XKCD comic about gravity wells:

    1. What about Mars gravitational influence? If it grips Phobos would it not influence a ship leaving Phobos? Still the points taken. I think we know little of Phobos. My guess is that it’s an astroid captured.

  4. Some over simplified numbers:

    Phobos escape velocity is about 40 Kmh (hardly worth mentioning), but it also orbits Mars at about 7,700 Kmh. Mars escape velocity is about 18,000 Kmh. To break orbit from Mars after almost “jumping” off Phobos , we “only” need to accelerate by around 10,300 Kmh (since we are already traveling 7,700 Kmh in Mars orbit)

    To break orbit from Mars after having landed on the planet, we need to accelerate (partially through the atmosphere) by just under the full 18,000 Kmh escape velocity (just under because at the Mars equator the planet is rotating at about 800 Kmh and a lift off from Mars would travel in the direction of rotation.

    Of course this only roughly describes the difference in acceleration required to break out of Mars orbit when comparing a Phobos landing to a Mars landing.

    As Gopher says, Doing a landing on Mars with the necessary rocket (and fuel) to get off it again would incredibly more complicated than simply (almost) “bumping” into Phobos and jumping off again. The difference in weight of the two missions would be huge, as would the size of the required rocket leaving Earth.

    1. And in doing so, you’d get some pieces of Mars and Phobos to bring back. A good ROI for such a mission!

    2. That is not how it works.

      A) Escape velocity declines drastically with distance. Mars’ surface escape velocity has no relevance to leaving Phobos.

      B) Escape velocity only applies to ballistics, i.e., one big push, no continued propulsion, so it is meaningless in the context of a rocket.
      The vehicle will not have to get anywhere near 18000 kmh, nor 10300 kmh when leaving Phobos. (I don’t know what speed they intend it to travel between Earth and Phobos, though.)

  5. Fantastic…I am not so familiar with such knowledge invested in so many bright commenteers , which I am overwhelmed,I simply can say I am not only proud but satisfied that we still have some element of surprise in our society paralell to fake personalities , not Bright enough to know the meaning of escape velocity,but still try to manage the people, ofcourse they are scientists shall we say ,but what kind , only GOD knows.

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