If I were to design a laboratory to answer questions about solar systems, I could hardly do better than TRAPPIST-1.
The system, only 39 light-years away, comprises a dark red sun orbited by seven rocks, worlds the size of the Earth, almost as if someone had designed an experiment in the formation of planets.
When the discovery was announced in February, it sent planetary scientists Amy Barr Mlinar, Vera Dobos and Laszlo Kiss to the moon.
All of us have waited our entire career to be able to take what we know about solar system processes and extrapolate to another system, "said Barr Mlinar, a scientist at the Planetary Science Institute." Here we can finally do it. " In a study in the journal Astronomy and Astrophysics Barr Mlinar and his colleagues looked closely at the geophysics of the seven worlds TRAPPIST-1, revealing places that could overflow with liquid water or boil with volcanic activity. the planets, d and e, are potentially habitable: under the right circumstances, they could sustain life.
Very little is known about the planets TRAPPIST-1, called the plane h in order of distance from their sun. They can see directly with our technology, but astronomers discovered them by measuring small dots in the light that emanated from their star when the planets crossed in front of it, a phenomenon that loved "in transit". By studying the frequency of these transits, the scientists were able to determine the length of the orbits of the planets and their distance from the star.
The discoverers of TRAPPIST-1 also determined that the six inner planets are locked in an orbital resonance, which means that the lengths of their orbits are related by a ratio of integers. Because of this, the bodies exert regular gravitational influences on each other. By measuring these influences, astronomers could determine the mass of the planets, something that is impossible to deduce only from the data in transit. This in turn allowed them to calculate the densities of the bodies comfortably.
With this scant information, Barr Mlinar and his colleagues set out to build a model of how these worlds could be. Having an estimate of the density of each planet allowed them to guess what the planets could be made of.
"It's common sense," he said. "As if your grandmother handed you a box of cake, you can say:" Given the size of this box and how much this cake weighs, it has to be a fruit cake ".
Dense planets like Mercury , Venus and the Earth are the fruit cakes of our solar system, composed of heavy iron and silicate rock. At the other end of the spectrum, there are worlds illuminated by a large proportion of water; for example, the moon of Jupiter, Ganymede, which is covered with ice. These same principles apply in TRAPPIST-1, assuming that this system behaves in accordance with our simplest scientific models (which, Barr Mlinar admits, is a great assumption).
Scientists also calculated the influence of tidal warming on each of the TRAPPIST worlds. As the planets revolve around their sun in an elliptical orbit, the thrust and gravitational pull create friction in their interiors, generating heat. This same phenomenon is responsible for the warming of the centers of the moons such as Europa of Jupiter and Enceladus of Saturn in our own solar system.
With this information in hand, planetary scientists could begin to characterize these extraterrestrial locations.
The TRAPPIST-1 system looks like ours, but in miniature. The star at its center, a red dwarf, is small and cold, but prone to violent attacks that send radiation into space. Its planets orbit closely, the most distant ends its circuit around the sun in just 20 days. This closeness means that the planets are probably blocked by tides; one side always faces the star, while the other is enveloped in constant darkness.
TRAPPIST-1b, the body closest to the sun, is a surprisingly low density planet and probably hosts a good dose of water. It is also likely to be subject to intense warming of the tides, which could generate volcanic activity. Barr Mlinar imagined a wet world where underwater volcanoes emit hot gases and molten rock and intense radiation hits the surface.
Its neighbor, TRAPPIST-1c, is much denser but similarly deformed by tidal forces; This rock and body rich in iron can also boast volcanoes. That is a bad omen for the potential habitability of the planet. But it is an exciting prospect for Barr Mlinar, since volcanic eruptions shed huge amounts of material into the atmospheres of their planets, and that material could one day be detectable by telescopes on Earth.
It's common sense. As if your grandmother gave you a cake box, you can say: "given the size of this box and how much this cake weighs, it has to be a fruit cake"
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In an initial analysis published In 2016, scientists reported that planets B and C have small, contained atmospheres, the kind that surrounds Earth, Venus and Mars.
The most distant planets in the system, f and g, are cold places that resemble low-density ice-covered worlds in our outer solar system, including Saturn's moon Enceladus and Jupiter's moon, Ganymede. And planet h is so light that theoretically it could be completely made of ice.
But the best real estate in the TRAPPIST-1 system are the planets d and e. These sit in the "Goldilocks zone," neither too close nor too far from the sun, where water can be liquid on its surfaces, and life could theoretically thrive.
Planet d receives enough sunlight that its effective surface temperature (assuming it lacks an atmosphere) is approximately 18C. Given its small size and low density, it is likely to be rich in water and may be covered by a global ocean. And since its interior is stirred by substantial amounts of tidal warming, it has enough geothermal activity to propel the complex chemistry in its oceans, creating conditions similar to Earth's oceans.
The most distant planet receives less sunlight, making it warmer as the South Pole in summer. But of all the TRAPPIST-1 planets, Barr Mlinar said it's her she would most like to visit. "I do not even have to think about it!" she declared. Specialist in frozen bodies, Barr Mlinar is attracted to this world where the effective temperature of the surface is near the melting point of ice.
"There could potentially be liquid water on the surface, there could be places where the ice is going to be really soft," she said. "That will give interesting ice tectonics."
Barr Mlinar warned that these descriptions of the planets are totally hypothetical, that they depend on insignificant data and a lot of assumptions. It will take much more research – probably with telescopes that do not even exist – to know what the TRAPPIST-1 planets really are.
Even so, theorizing about the geophysics of these worlds can be useful, he said. For example, the knowledge that TRAPPIST-1c can be volcanically active could guide the search for molecules in its atmosphere by astronomers.
Not to mention that it's great. Seen through the telescopes of astronomers, these planets are only "points of light, or even points of light," he said, "only signals in a curve of light, measurements in an instrument."
But apply some basic principles of planetary science, and those pieces of data merge into physical worlds: active or inert, hostile or attractive. We can begin to imagine the feet on that alien ground.
As Barr Mlinar said: "Help everyone in the community see these planets as places where the types of processes that operate in our solar system also operate."