NASA's TESS telescope discovered Earth 2.0.

Brief introduction: This paper briefly introduces TOI-700 star and its three planets, and explains the importance of liquid water to livability. Scientists speculate on the possible climate of this star by building a model.

Artist's impression of planets outside the habitable zone of stars.

A group of NASA exoplanet astronomers who study planets around other stars contacted me to attend a secret meeting and told me a planet they were interested in. Because my professional field is simulating the climate of exoplanets, they asked me to determine whether this new planet is suitable for living and whether there may be liquid water.

These colleagues from NASA, Josh Slider and his students Emily Gilbert, Tom Buckley and Eliza quintana, while studying the data of TESS (the Exoplanet Ling Xing Survey Satellite), discovered a planet the size of the earth that may be the first time observed by TESS, and there may be liquid water on its surface. This is exciting news, because this new planet is relatively close to the Earth, and its atmosphere will be observed through the James Webb Space Telescope or a large ground telescope.

Planets in the livable zone

The host star of this planet discovered by Gilbert's team is called the exoplanet Ling Xing Survey Satellite's Interest Star 700, or TOI-700. Compared with the sun, it is a small and dim star, the size is 40% of the sun, and the brightness is only about 1/50 of the sun. It is located at 0/00 light-year distance from the Earth/kloc in the constellation Swordfish, and can be observed in our southern hemisphere. Relatively speaking, the nearest star, proxima centauri, is 4.2 light years away from the Earth. To know these distances, it will take nearly 20,000 years for the fastest spacecraft (Parker Solar Probe) to reach proxima centauri.

There are three planets around TOI-700: B, C and D. Planet D is the same size as the earth, located in the livable zone of stars, and orbits TOI-700 once every 37 days. My colleagues hope that I can use the known characteristics of stars and planets to build a climate model of star D. Planets B and C are the size of the earth and mini Neptune respectively. But their orbits are closer to the main star, and the starlight they receive is 5 times and 2.6 times that of our earth from the sun, respectively. In contrast, Venus has a dry surface, the temperature is about 860 degrees Fahrenheit, and it receives twice as much sunlight as the Earth.

Until about ten years ago, astronomers only knew that there were two planets with different sizes in the livable zone: Earth and Mars. However, in the past ten years, thanks to the ground-based telescope and Kepler project, astronomers have discovered about 12 earth-sized exoplanets (they also searched for exoplanets from 2009 to 20 19, but now they have retired). They are located in the livable zone of their host stars, and their volume is half to twice that of the earth.

Although the number of small exoplanets discovered so far is relatively large, most stars are 600 to 3,000 light-years away from the Earth-too far and too dark for detailed follow-up observation.

Why is liquid water important for livability?

Unlike Kepler, TESS's task is to find the planet closest to the sun: bright enough for subsequent observation.

TESS has observed more than 1500 candidate planets since April 20 18. Most of them are twice the size of the earth and orbit for less than ten days. It takes 365 days for the earth to go around the sun. Therefore, these planets get much more heat from the sun than the earth. The earth is too hot for liquid water to exist on their surfaces.

Liquid water is very important for livability. It provides a medium for the interaction of chemical substances. Although there may be alien life under high pressure or high temperature, such as extreme microorganisms found near fire and water vents or microorganisms found half a mile below the ice sheet in western Antarctica. Humans have been able to directly detect these extreme environments, so these discoveries are possible, but these alien life can't be found in space.

When people are looking for life or livable environment outside the solar system, they rely entirely on remote observation. Liquid water on the surface will create a livable environment and may promote the emergence of life. Then these life forms interact with the atmosphere above them, and there are life features that can be detected remotely by telescopes on earth. These characteristics may be terrestrial gas components (oxygen, ozone, methane, carbon dioxide and water vapor), or the gas components of the ancient earth 2.7 billion years ago (mainly methane and carbon dioxide, without oxygen).

We know that the planet where this happened is the earth. Therefore, the goal of astronomers is to find a planet about the size of the earth, orbiting a star with liquid water on its surface. These planets will become our main goal to explore the livable world and life characteristics outside the solar system.

The three planets of TOI 700 system revolve around a small and cold M dwarf. TOI-700d is the first Earth-sized planet discovered by TESS in the livable zone.

Possible climate of TOI-700d planet

In order to confirm the existence of planet D around TOI-700, Gilbert's research team needs to confirm it through data observed by other telescopes. TESS detected the planet before it passed through the star, when the light of the star weakened. However, this light attenuation may also be a false active signal generated by instrument noise or mutual shielding of the binary system behind it. Joey Rodriguez of the Center for Astrophysics at Harvard University made an independent observation. Rodriguez and his team confirmed the real existence of TOI-700d planet observed by TESS through Spitzer telescope.

My student Gabriel engelmann-Sousa and I used our modeling software to determine the possible climate types on TOI-700d. Because we don't know what kind of gas may exist in the planet's atmosphere, we use climate models to analyze the gas composition on its surface that supports the existence of the ocean. With the help of my long-term collaborator Eric Wolff, engelmann-Sousa has tested a variety of atmospheric components, including the current atmospheric components of the earth (77% nitrogen, 265,438+0% oxygen, methane and carbon dioxide), the atmospheric components of the earth 2.7 billion years ago (mainly methane and carbon dioxide), and even the atmospheric components that might have existed on Mars 3.5 billion years ago (a large number)

Based on our model, we found that TOI-700d may be a livable planet if its atmosphere contains methane, carbon dioxide or water vapor. Now our team needs to confirm these hypotheses through the James Webb Space Telescope.

Bacteria living in such a harsh environment as the geothermal basin in Yellowstone National Park provide clues for finding livable areas on other planets.

Novelty world and its climate

The climate simulation completed by NASA team shows that the atmosphere and gas pressure similar to the earth are not enough to realize the existence of liquid water on its surface. If we discharge the same amount of greenhouse gases into TOI-700d, the surface temperature will still be below zero.

At present, there are oceans under our earth's atmosphere, because our stars are bigger and brighter than TOI-700. One thing is certain: all the models of our team show that the climate of the planets around those small and dark stars is completely different from what we see on earth.

The field of exoplanets is in a transitional period from finding them to understanding their atmospheric characteristics. In the history of astronomy, new technologies have brought new discoveries of the universe, including surprises like hot Jupiter and small Neptune, which are not available in our solar system. At this stage, it is necessary to observe the atmospheres of these planets to see if they have the necessary conditions to support life activities.

reference data

1. Wikipedia

2. Astronomical terminology

Translation: Yilan

Author: RAVI KUMAR KOPPARAPU

Please also get authorization for reprinting, and pay attention to maintaining integrity and indicating the source.