How on earth can teachers answer that question - and it's one that will be asked a lot after this summer's news of Martian fossils and of ice on one of Jupiter's moons. Nicholas Pyke reports on the latest astronomical controversies.
No one yet knows what to make of the microbes from Mars. The bacteriological life supposedly fossilised on a Martian meteorite in Antarctica is a matter for considerable scientific scepticism and promises to be so well beyond the review of the national curriculum in 2000.
Ditto the subsequent news of freezing water on a moon near Jupiter, another indication that there might be extraterrestrial life.
These being the summer months, the speculation has been intense. But the new signs of unintelligent life are not likely to figure on the school timetable. Which is perhaps a good job, as it seems that few science teachers are in much of a position to deal with the specialist complexities of astronomy.
There are elements of the cosmos prescribed in the national curriculum. Such things as the life-cycle of stars and the origins of the universe have proved hugely popular - a popularity that is all the more notable in the light of declining levels of interest in science as a whole. According to the Royal Astronomical Society, however, schools are not in a good position to exploit what is, by any standards, a difficult subject.
"It certainly is a bit of a problem for teachers who are trained in physics but haven't included any astronomy or astrophysics in their own learning programme," says Jacqueline Mitton from the RAS. "I can say from personal experience and also from the work of the RAS that there's a demand from teachers both for scientific knowledge in the astronomical area and for help with teaching ideas."
Dr Julie Cave boasts a rare combination of experience in both astronomy and physics teaching. Formerly an astronomer specialising in Mars at University College, London, she says: "The majority of teachers have little or no formal training in astronomy. And in order to teach something with confidence you need to have looked at it at a higher level than the classroom.
"It's not that the teaching we're getting is wrong. But we're not taking full advantage of something that kids find fascinating. Getting all the detective work together, for example; learning how to judge things like the size and heat of a star when all you have to go on is light emission.
"There are quite a lot of difficult concepts. Unless you have a strong background in physics and astronomy it's quite hard answering the pupils' questions. Many teachers are aware they can't give good explanations. How we know the temperature at the centre of the sun, for example; or how we know the age of the universe."
Like many other expert observers, Dr Cave is cautious about the lump of Martian rock, labelled ALH84001, and the "fossils" said to resemble terrestrial bacteria. The meteorite that wound up in Antarctica is reckoned to be at least 200 million years old, although for the past 13,000 it has resided on Earth. Attention will focus on whether the fossils could have been created in that time.
As New Scientist magazine pointed out, this is not the first time that claims have been made for Martian meteorites and signs of life they carry. In 1961 something like fossilised algae was discovered on one, only later to be dismissed as the product of earthly contaminants including, says the New Scientist, ragweed pollen.
Yet, quite apart from this, there is some interesting and reliable evidence there may once have been life elsewhere in the solar system. The new pictures of Europa, a moon of Jupiter slightly smaller than our own moon, suggest that the fractured icy crust on its surface may be floating on a bed of liquid water or slush - the essential precondition.
Even Mars, a dry and bitterly cold planet with a thin carbon dioxide atmosphere and frequent dust storms may once have been a much wetter and more hospitable place, says Dr Cave. The images of the planet obtained by NASA (the American National Aeronautical and Space Administration) show features resembling huge dry river beds, rivalling the Mississippi for scale.
"The number of water-formed features means that water was once much more abundant on or near the surface of Mars," says Dr Cave. "This in turn means that the atmosphere must once have been much more dense to allow liquid water to persist. Such an atmosphere would mean that the surface was warmer (a thick atmosphere would trap more of the sun's heat) and several scientists have suggested that these warmer, wetter conditions existed early in Martian history for a period similar to the time during which life started to develop on Earth."
The planet has however lost its thicker atmosphere, with some believing that most of the water infiltrated the surface of Mars, forming reservoirs of ground ice (permafrost) instead. In recent years, she says, scientists have been considering the possibility that some forms of life started to evolve either in ice-covered lakes or in thermal vents created by volcanoes.
The latest evidence from the meteorite is more equivocal. Some dispute the rock's Martian origins. Others suggest that the patterns could have been produced geologically or as the result of biological processes on Earth. Nor has it gone unnoticed that the scientists who presented the meteorite to the world's cameras are from NASA - which has been in particular need of funding for the next stage of its space programme.
The RAS in Cambridge runs regular in-service training courses. Dr Cave and her astrophysicist husband David Wonnacott will be offering physics teachers a basic grounding in astronomy later this autumn at Kingston University.