Most of us have seen films about extraterrestrials: Alien, Close Encounters of the Third Kind, ET: The Extraterrestrial. We are thrilled by the notion that there may be “something else out there”, even if Hollywood often paints that “something else” as predatory and terrifying.

But how would we really greet and treat an alien visitor to Earth? Rather than the Men in Black, they would most likely be greeted by the men in white coats, armed with instruments to extract DNA (if that is what aliens have in their cells), scalpels, myriad scanners and test tubes.

Jocelyn Bell Burnell, the astrophysicist and discoverer of pulsars (rotating neutron stars that emit regular pulses of electromagnetic radiation) made headlines in July when she suggested at the Euroscience Open Forum in Dublin that we will find proof of life elsewhere in the universe within the next century. Although Bell Burnell and her supervisor, Antony Hewish, did not believe that the regular signals they detected from distant pulsars were signs of intelligent life, they labelled the first signal LGM-1, which stood for Little Green Men 1.

But would we even recognise life from another planet? Life on Earth is carbon-based, water is crucial and there are six essential elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur (CHNOPS). In 2010, it was announced that a life form capable of living off arsenic - normally very toxic - had been discovered, though that claim has recently been disputed. Life that exists on Earth in very hostile environments is given the collective name extremophiles. But these are mostly bacteria or low-level life forms. Intelligent, sentient life from another planet would be a whole different issue.

The likelihood of an alien visiting Earth in a spaceship is remote. The distances between galaxies make such travel impossible within a human lifespan. Films are full of theories about jumping across light years using wormholes, but such structures do not, to our knowledge, exist in a way that would allow them to be used for interstellar travel. It may, however, be possible to detect radio signals that indicate we are not alone.

The most interesting question for the classroom is moral and ethical debate about how you would treat an alien visitor. Using the analogy of pests on Earth, we know that people are far less worried about killing bugs and insects than other, more cuddly animals. So what if our alien visitor was a small, ugly, cockroach-like creature? What if it looked dangerous and was unable to communicate with us? How would the military and scientists treat it? Would we employ our own moral and ethical stances with something that is not of this world?

In science fiction, writers have thought long and hard about this question. They have introduced rules about how we should interact (or not) with alien life forms. Star Trek has its “Prime Directive”, for example, the guiding principle of the United Federation of Planets, which states that there should be no interference with the development of any alien civilisation.

Sentient, intelligent life is likely to have developed a means of communication with humans, most likely a form of mathematics. And how we would treat such life forms could be vital to our future survival.

While conspiracy theorists insist that aliens have and probably still do visit Earth, no government acknowledges the existence of intelligent life in our solar system, though they do not rule out intelligent life somewhere in the universe. Nasa famously announced in 1996 that there was probably life on Mars when they looked at a meteorite found in the Antarctic and identified it as having been blasted from the Martian surface. Deep in its structure was possible evidence of fossilised microbial life.

In June 1947, a small-town newspaper printed a story about a crashed alien spacecraft in Roswell, New Mexico, in what is now infamously referred to as the Roswell Incident. A local rancher, William “Mac” Brazel, came across debris strewn over a large area, which was recovered with the help of personnel from the local military airbase. Walter Haut, head of public information at the airbase, announced that a flying saucer had crash- landed. Soon afterwards, the story was debunked. The space junk was apparently the remains of a military weather balloon. But the rumours never stopped and there was even a video tape (proved to be a hoax) of the alleged alien dissection.

Would we really imprison or dissect an alien life form? Could we honestly let them run free? That could expose humans to terrible danger - not from any evil intent by the alien but from the microbes it may have brought with it.

But wondering about life on other planets is not just the preserve of modern times. On 25 August 1835, the New York Sun created the Great Moon Hoax, printing the first of a series of articles about the moon, which claimed it was inhabited by winged creatures, bipedal beavers and unicorns.

Perhaps more to the point is that we do not like to think we are alone. Scientists continue to search the vast expanse of our universe with radio telescopes, looking for patterns in signals that cannot be explained naturally. The Search for Extraterrestrial Intelligence (Seti) started as an American government-funded programme. That funding has since stopped, but the search through the Seti Institute continues. And under the guidance of the International Academy of Astronautics, Seti does have a set of protocols for what we should do if we detect intelligent life. If such a signal is found, Seti advises that “a confirmed detection of extraterrestrial intelligence should be disseminated promptly, openly and widely through scientific channels and public media”, with the body that made the discovery having the privilege of making the first public announcement.

How would your science class manage it? And what risks might they have to consider? What would be their prime directive and why? It may well be that governments across the world already have a protocol in place for dealing with the appearance of an intelligent life form; if so, it is likely to be classified information. But setting your students the task can lead to lively and thought-provoking debate.

James Williams is a lecturer in science education at the University of Sussex’s School of Education and Social Work. The Seti protocols can be found at www.setileague.orgiaasetiprotdet.htm

What else?

Key stage 1: Outer space

Explore the final frontier with a Year 1 topic plan from comenius.

Key stage 2: Alien arithmetic

It’s aliens vs maths in a project from nicolawaddilove.

Key stage 3: Are they out there?

An assembly by grahamcolman.

Key stage 4: Universal ideas

Attitudes towards space over the centuries from rubberchicken2.

Key stage 5: To infinity

Discover how the universe is growing in a lesson from iop.

Find all links and resources at www.tes.co.ukresources047.