Spare a thought for the Earth’s tiniest astronauts, whose journey to another planet will end in a fireball on Sunday night or Monday.
That's when the Russian probe Phobos-Grunt on which they were launched crashes back into the Earth’s atmosphere. It is an unheroic end for what might have been a great mission.
These astronauts really are very small. Called tardigrades or, for obvious reasons, water bears, this is Hypsibius dujardini, microscopic, water-dwelling animals that can live everywhere from the polar regions to the deep sea via any clump of lichen you happen to pass. I wrote about them here some time ago, recording their achievement in surviving exposure to deep space on board the Space Shuttle.
Tardigrades are extremophiles, content to live in environments hostile to most life. And they were chosen to represent life in what would have been a fascinating study. They were included in a capsule created by the Planetary Society, a cylinder 5½ centimetres across and weighing just 88 grams that was included in the packages that Phobos-Grunt was to take into the orbit of Mars by late 2012 and then to the Martian moon Phobos in February 2013.
Why send tardigrades there? Because Phobos-Grunt was designed as that special, rare and very difficult thing, a sample and return mission. It was intended to scoop up some of the soil of Phobos (hence its name Grunt, which though unattractive in English means soil in Russian) and then bring it back, sending a return capsule of soil and the LIFE capsule into the atmosphere for a hard landing in August 2014.
None of this is going to happen now. Some two hours into its journey on 9th November 2011, while still in its low ‘parking orbit’ above Earth, something went wrong with the rocket systems designed to push the probe into deep space. Phobos-Grunt was always a hefty mission – at some 13 tons, it’s the largest probe launched for a long time, mostly fuel but also a Chinese Mars probe called Yinghou-1. Initially Phobos-Grunt’s distress was labelled ‘a non-standard situation’ by the Russian Space Agency Roscosmos. This became ‘a serious flaw’ some days later as attempts to reload the software – to turn it off and on again, essentially – failed. It seems that a hardware error fatally undermined the rocket systems. Phobos-Grunt stayed in its low Earth orbit.
Its failure has been visible, if you know where to look. The fantastic astrophotographer Thierry Legault not only saw but made a video of the satellite as it passed within the reach of his observatory near Nice, France, on New Year’s Day 2012. You can watch the film here. More recently, the Fraunhofer tracking radar TIRA picked up Phobos- Grunt in its death agonies. It will have burnt up, or crashed, by sometime tonight or tomorrow.
Why try to go to Phobos at all? The failure of the mission has cost £107 million in direct costs to Roscosmos and other participating agencies, excluding the Chinese Space Agency, which does not publish such things. It’s an expensive firework for very few people to see. And Phobos is an odd destination, an ugly, potato-shaped moonlet of Mars, very small and dominated by one feature, the Stickney Crater. For those of a certain age, Phobos looks remarkably like the Death Star in the first Star Wars film.
It is almost certainly a captured asteroid, presumably perturbed from its original orbit in the asteroid belt and then drawn to Mars by the force of the planet’s gravity. It is indeed getting closer to Mars all the time, as opposed to our Moon which is leaving us by an inch or so every year.
The European Space Agency Mars Express mission recorded these images of Phobos recently during an unusual alignment between with Jupiter. In these images, Jupiter looks tiny. It is, of course, impossibly the larger object.
Nice pictures, but why spend a hundred million pounds to (not) get there? Remote surveys of Phobos indicate that it has a very low density, suggesting that it is made up of rubble and contains large interior voids. It may well be a ‘primitive’ asteroid left over from a very early period in the history of the Solar System, and an analysis of its regolith could tell us a great deal about conditions prevailing at that time. Phobos is also scored by strange grooves thought to be the trails left by ejecta thrown off from Mars. If so, then Phobos might harbour Martian meteorites as well. Finally, the Phobos-Grunt mission was an opportunity to test the kind of sample-return mission that would transform our ability to study Mars itself. This was probably Phobos-Grunt’s biggest prize.
Okay, but why send water-bears there and back? That is part of a different project, one that reaches back through the Space Shuttle era and to the later Apollo missions. Apollo 16 and Apollo 17 both included Biostack packages, groups of single-celled organisms, plant seeds and animal eggs that were sent to the Moon so as to investigate the effects of the deep space environment on their survival. It was found that the animal eggs especially did not do well. Very few of the brine shrimps (Artemia Salina) reached maturity and none developed normally. Tardigrades first went to space as part of the same effort to understand survival in this dreadful habitat in 2007.
The Phobos-Grunt capsule had a related but different purpose. There is a theory called transpermia that postulates the possibility of life spreading between terrestrial bodies using asteroids as a form of transport – Micromegas and friends do the same in Voltaire’s novella of the same name, and so do the characters in James Palumbo’s Tancredi. More seriously, it is the central issue with the meteorite ALH001 which some scientists assert contains life from Mars. Is it possible for anything to survive that journey?
The tardigrades were going to put transpermia to the test. They would go to Phobos and then come back in the return capsule, their cylinder strengthened to survive the hard landing and also to avoid contaminating Mars or Phobos were the probe to crash into either body.
Now we’ll never know.
Mind you, the tardigrades might survive the fires of re-entry. Then they will teach us something else.