Scientists are discovering an increasing number of planets in other galaxies that resemble our own. What betrays them? Expert Jérémy Leconte takes a look.
“No one really has the same expectations or criteria for a planet to be what you call Earth-like,” says Leconte. For some, a just rocky planet is enough. This means a solid surface, unlike gas giants like Jupiter or Saturn.
To achieve this, scientists first measure the radius of the planet as it passes in front of a star, which allows them to estimate its size. To calculate its mass, they look at how much the planet’s orbit causes the star to “wiggle”. Using these calculations, they can then determine the planet’s density, sorting the solid worlds from the gaseous blobs.
“But you still have rocky planets at 2000ºC, where you’re actually melting the surface,” adds Leconte. These so-called lava ocean planets are not exactly livable. “Not for us anyway.”
The next step is to see if the planet is temperate, with a climate mild enough to support liquid water on the surface. This is revealed by the amount of light a planet receives, as well as its orbit.
However, this is still not enough for some scientists to consider an Earth-like planet. They want to know if there is an appropriate atmosphere. For this, they again look at the planet transiting in front of a star. As certain gases block certain wavelengths of light, incoming light around a planet will be imprinted with the atmospheric signature.
The most difficult thing is to know if there is really liquid water on the surface. The density of a planet could give clues, but the calculations must be extremely precise. Indeed, even on oceanic planets like ours, where water covers 71%, it represents only a tiny fraction of the total mass. In other words: the radius of the Earth is about 6,000 km, while the oceans are, on average, about 3.5 km deep.
Yet, with the above knowledge in hand, everyone would be satisfied. “Unless you really want to see the aliens there,” Leconte says, “when people think of Earth, having a rocky planet that’s temperate, has an atmosphere, and has liquid water, we we are there.”
Review of exoplanets
In the WHIPLASH project, Leconte has developed a new suite of tools and techniques to analyze the atmospheres of distant planets.
Through this project, WHIPLASH has created a new framework for understanding the physics and composition of exo-atmospheres, based on an innovative 3D planetary atmosphere simulator.
With the recent launch of the James Webb Space Telescope (JWST) and the European Space Agency’s Ariel mission scheduled for the end of this decade, scientists will have ultra-high resolution features of distant planets to study.
This could help learn more about the exoplanets around TRAPPIST-1, a star just 40 light-years from Earth, including the presence of liquid water on the surface.
Mission to a new Earth?
The closest star system to ours is centered around the red dwarf star Proxima Centauri. And just over four light-years from Earth, Proxima Centauri b is our closest Earth-like exoplanet. So how soon can we expect a mission to get there?
Even traveling at 10% of the speed of light, the journey would take another 40 years. “There are crazy ideas about how to send very light probes that would be pushed by a laser,” remarks Leconte. “But even then, I think it’s just science fiction. So it’s not anytime soon, I would say.”
Opinion: Scientists may have discovered an Earth-like planet. Let one of them tell you about it.
Quote: How do we know that distant planets look like Earth? (2022, October 24) retrieved October 25, 2022 from https://phys.org/news/2022-10-distant-planets-earth-like.html
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