Humanity will not migrate to an Earth twin: Astrophysicist Michel Mayor says there is no Planet B

Somewhere in the vast expanse of the observable universe, a planet may be orbiting a star 30 light-years away from Earth, with conditions that could, in some respects, resemble those on our own planet. On the scale of the Milky Way, that is practically in our cosmic neighborhood. Yet, with the technology currently available to humanity, such a journey would take an extraordinarily long time, potentially hundreds of thousands or even millions of years.

This example illustrates the paradox at the heart of humanity's quest to find other Earth-like planets: the universe may be full of worlds that seem to offer what we need, yet they could remain forever beyond our reach.

Swiss astrophysicist Michel Mayor, who shared the 2019 Nobel Prize in Physics with Didier Queloz for the discovery of an exoplanet orbiting a Sun-like star, believes humanity must come to terms with this reality.

He made these remarks at STARMUS VIII, held on the Spanish islands of Tenerife and La Palma. Co-founded by Armenian astrophysicist Garik Israelian and British astrophysicist and legendary Queen guitarist Brian May, the festival once again brought together leading scientists from around the world to discuss science.

“Humanity Will Not Migrate to an Earth Twin” was the title of Mayor's keynote address at the festival. He warned his audience against looking to other planets for an escape from the problems humanity itself has created on Earth.

“We do not have a planet B. We have to take care of Earth.”

Mayor also addressed two important questions: whether large-scale settlements could be established on Mars and how common Earth-like planets are in our galaxy. Although astronomical discoveries in recent years have radically transformed our understanding of planetary systems, he stressed that finding a potentially habitable planet does not mean humanity will ever be able to reach it.

Why Mars is no second Earth

In recent years, the idea of moving millions of people to Mars, promoted by several wealthy entrepreneurs, has become a subject of widespread debate. But how realistic are such ambitions? Mayor urged his audience to consider the actual conditions on the Red Planet.

Mars has an atmospheric pressure roughly one hundredth that of Earth. Its atmosphere consists primarily of carbon dioxide, argon and other gases, with virtually no oxygen suitable for human respiration. Its average surface temperature is around minus 60 degrees Celsius. Extreme cold, powerful winds and cosmic radiation pose additional challenges, while Martian soil is unsuitable for conventional agriculture without substantial treatment.

Establishing a permanent human presence there would therefore require pressurized habitats, protective domes or underground facilities capable of shielding people from radiation, extreme cold and other environmental hazards.

“Do you really dream of going to this surface?” Mayor asked, challenging optimistic visions of large-scale Martian settlement.

In his view, the problem is not simply the difficulty of building habitats or growing food. The broader question is whether humanity should regard another planet as a realistic refuge if, for one reason or another, Earth becomes uninhabitable.

A galaxy full of planets

The prospects of discovering other planets are far more promising than the possibility of one day moving to them.

The Milky Way is approximately 100,000 light-years across and contains hundreds of billions of stars. For much of the history of astronomy, humanity was unaware of the existence of planetary systems beyond our Solar System. However, particularly over the past decades, as our understanding of star formation has deepened, it has become increasingly clear that planet formation is a natural consequence of this process.

Observations of young stars have subsequently provided compelling evidence that they are often surrounded by disks of gas and dust from which planets can form. Instruments at the Atacama Large Millimeter/submillimeter Array (ALMA) allow astronomers to study these disks in unprecedented detail.

Today, the question is no longer whether other planetary systems exist. Scientists are now trying to determine how common Earth-like planets are in the universe and how many of them might have conditions favorable to life.

For a planet to be considered potentially habitable, it must orbit its star at a distance that, provided other necessary conditions are present, allows liquid water to exist on its surface. If a planet is too close to its star, it may be too hot; if it is too far away, it may be too cold. This range of distances is known as the habitable zone. However, simply being located within this zone does not mean that a planet is inhabited or even possesses all the conditions necessary for life.

How scientists find distant worlds

Because planets are generally much fainter than the stars they orbit, astronomers have developed indirect methods to detect them.

Mayor explains that one of these is known as the Doppler or radial velocity method. It makes it possible to measure the slight movements of a star caused by the gravitational influence of a planet orbiting it. By observing changes in the star's velocity, scientists can infer the presence of a planet and estimate its mass.

Another method, known as the transit technique, detects the slight dimming of a star when a planet passes between the star and the observer. The amount of light blocked can reveal the planet's size, while repeated transits can help determine its orbital period.

NASA's Kepler space telescope demonstrated the effectiveness of this method. By monitoring more than 100,000 stars in a fixed region of the sky, it detected periodic dips in their brightness, indicating the presence of orbiting planets. Among its discoveries were planetary systems in which several planets orbit the same star.

The scientist notes that the two methods complement each other: transit observations provide information about a planet's size, while radial velocity measurements help determine its mass. By combining these measurements, researchers can estimate a planet's density and gain insight into its likely composition.

Mayor also emphasizes the importance of studying planetary atmospheres as a promising direction for future research. When a planet passes in front of its star, a small portion of the starlight travels through the planet's atmosphere. Analyzing changes in the light spectrum can reveal information about the atmosphere's chemical composition.

Such observations can help scientists determine whether distant planets have atmospheric conditions compatible with life.

Finding an Earth twin is not the same as reaching it

Despite the growing number of exoplanet discoveries, Mayor cautions against confusing theoretical astronomical possibilities with practical feasibility.

Even a planet that appears promising for life could be so distant that reaching it would be impossible for humanity. To illustrate the scale of this challenge, he asks his audience to imagine an Earth-like planet located 30 light-years away.

Compared with the Milky Way's vast expanse of 100,000 light-years, this distance may seem relatively small. Yet it is approximately one billion times the distance between Earth and the Moon.

At the speeds achieved by spacecraft used in the Apollo missions, reaching such a planet would take millions of years.

Mayor explains that increasing a spacecraft's speed would require enormous amounts of energy. The challenge is not simply to travel twice as fast, but to achieve velocities far beyond the capabilities of today's human spaceflight technology.

He argues that even if scientists discover a nearby planet with conditions favorable to life, that would not make it a realistic destination for humanity.

In Mayor's view, this is a fundamental limitation that must be taken into account in any discussion about the future of space exploration. The universe may contain countless worlds, but their existence does not guarantee that humans will be able to travel between them.

There is no Planet B

The search for exoplanets has radically expanded our understanding of humanity's place in the universe. Scientists now know that planetary systems are widespread, while increasingly sophisticated instruments allow them to study worlds that may resemble Earth in certain respects.

Yet an enormous gap remains between discovering a potentially habitable planet and establishing a human settlement there.

“If Earth begins to become uninhabitable, humanity will have no possibility of emigrating to another exoplanet,” Mayor says.

He notes that the search for other planets continues to be of great scientific value, offering opportunities to understand how planets form, how their atmospheres evolve and whether life could exist elsewhere in the universe. However, Mayor makes clear that this research cannot replace our responsibility to protect the only home we have: Earth.

“We have to take care of Earth. There is no Planet B”.

The Armenpress coverage of the STARMUS festival is supported by Team Telecom Armenia.