The first of two virtual conferences today was at the Royal Astronomical Society, by the Lord Rees of Ludlow, the society’s president from 1992 to 1994.

A brief introduction was given by executive director Philip Diamond, who announced that it was the last in their 2021-2 lecture series.

Rees is a former Master of Trinity College, Cambridge. He said that the college looked much the same three centuries ago as it does today. Newton’s legendary apple tree incident occurred when he was sent home during the 1665 plague outbreak. Sadly, none of the students put into lockdown during the COVID pandemic have had similar moments.

Rees proudly displayed his photograph of the lunar surface, autographed by seven astronauts who had been there. He noted how rapidly space exploration had progressed, from the launch of Sputnik in 1957, to dogs, then Yuri Gagarin, then the moon landing in 1969. Today only the elderly, such as his lordship, can actually remember watching the moon landing when it first happened. He and his contemporaries firmly expected to have conquered Mars within another twenty years. Alas we are still waiting.

Rees discussed the book The End of Astronauts which he co-authored with Donald Goldsmith. Artificial intelligence has become greatly more sophisticated with each decade since the time of the Apollo program. Miniaturised probes are already exploring much of the Solar System, especially Mars. Perseverance can navigate around rocks, whereas Curiosity needed to call back for instructions. The only downside is that the shear amount of time needed to travel to the outer planets often means that the probe’s technology is already obsolete by the time it arrives to start its survey. With each advance in artificial intelligence, the practical case for sending humans into space gets weaker. Robots can simply hibernate along the journey whereas humans need to sleep, eat and breathe. Also, fundamentally, they are disposable. NASA’s astronaut projects since Apollo have been limited to the International Space Station and the Hubble telescope. They are constrained by political pressure, especially since the Challenger disaster. Although this only represents a 2% overall failure rate, which would easily be acceptable in other fields, the public attitude towards NASA was damaged irreparably.

In a “terrifying” speech to a thousand GCSE students last month, Rees asked how many would actually endure the long journey to Mars. Only half would, but curiously all would be willing to send someone else away. One in particular was put off by the notion of a forty-minute delay in communications with Earth – a stark reminder of the change in expectations compared to the age of exploration by sea.

Rees believes that from now on state-funded scientific exploration of space is best accomplished by unmanned machines, while human journeys should be the preserve of prize-seekers in the private sector (where a greater level of risk is tolerated). He would support the efforts of Elon Musk and Jeff Bezos over any more missions by NASA. He recalled that the former wishes “to die on Mars, but not on impact”, which could be plausible if he lives another fifty years. The term “space tourism” is highly misleading. This is a dangerous sport for intrepid exploration. Mass emigration to escape Earth’s problems should not be expected for there is simply nowhere habitable.

The professor then moved on to the possibility of life elsewhere. He said that settlers on Mars would be beyond the clutches of regulators on Earth, and that over time their progeny could diverge into a post-human species. Astronomers, he thought, have a special perspective – humans are not the pinnacle of evolution, for our sun has another six billion years to go. We could see a move from Darwinian evolution to secular intelligent design, so that by the time Earth dies the intelligent life on the planet will not resemble us at all. There is a debate among philosophers and neurologists as to whether AI can be truly self-aware. If machines were zombies then we wouldn’t value their experiences. The motives of the post-humans are, at this point, reserved for speculative fiction, though most expect that they would be expansionists. Even if life originated on Earth it need not remain a trivial feature of the cosmos – humans could found a galactic diaspora. Colonisation would take less time than has already elapsed since the Cambrian explosion.

The topic of life on other worlds has been hugely exciting for astronomers in the past twenty years. Nearly all stars are orbited by a retinue of planets. The first exoplanet was discovered in 1992, with several thousand more coming since. Planets are not observed directly, but detected by their effect on their stars. The brightness of a star is briefly dimmed when a planet moves in front of it. Kepler used this method to find several thousand stars with planets around them. The case study of TRAPPIST-1, discovered in 2000, shows a “miniature system”, the innermost planet having an orbit of one Terran day and the outermost an orbit of two weeks. Four of them are within a habitable zone that in principle could allow the existence of water, thus supporting life. It is frustrating that we cannot see planets directly, though in theory we could with a sufficiently large telescope. The European Extremely Large Telescope is planned to have a mirror thirty-nine metres wide. The James Webb Telescope is smaller but has the advantage of viewing infrared. The differing shades of blue on Earth could indicate the presence of oceans, continents and an atmosphere, while the time taken for each pattern to reoccur would indicate our rotation period.

In summing up, Rees said that we understand evolution but not the origin of life. Evidence of civilisation on other planets might only exist for a short time, and not be synchronised with that on Earth. Life may not yet have evolved, or could have already been superseded by machines. If the search for extraterrestrial intelligence fails then we can be less cosmically modest, but absence of evidence is not evidence of absence.

Following the presentation there remained a few minutes for questions and answers.

Does what you’ve said imply the end of astronauts as a profession?

I can’t predict more than fifty years ahead. We think human spaceflight should be left to private adventurers. Robots are better for state efforts.

Will there be a replacement for chemical rocket engines?

It’s certainly conceivable. Nuclear can provide low thrust for long periods. Ground lasers can push a small spacecraft by sail.

Will the first human on Mars inevitable contaminate the biosphere?

We have to be very careful, treat Mars like the Antarctic. Also, bringing organic material back could contaminate Earth.

Which planetary body has the best potential for life?

Looking under ice is obvious. Any evidence of life on other planets could help explain the origin of life on Earth. If life originated twice independently within the same star system it’s probably widespread.

What are the prospects for manufacturing probes in space to keep the technology up to date?

The Space Station has done some research and development. We would like to build a telescopes in space with an iterferometer. It should be a target for the 2068 centenary. Building solar panels in space would be good – you get ten times the power per square metre compared to the sunniest spot on Earth.

FURTHER READING

• The Lord Rees of Ludlow at TheyWorkForYou
• The End of Astronauts
• Martin Rees homepage