Earth-sized Planet Discovered

Are we alone? This question most often perplexes scientists. Even the general people wonder on it. The question is about the existence of life other than the Earth. We hear about the extraterrestrial lives, most often called aliens, in science fiction books and science-based films. But do they really exist? Nobody knows. The universe consists of millions of galaxies and there are millions of stars in each galaxy. Our Sun is not extraordinary, but a general star in the Milky Way galaxy. Many stars must have planetary system like our solar system. Thus, technically it is possible that there may be civilizations in other star systems. But the stars are far away from us and so we are not able to locate them. For example, our nearest star Proxima Centauri is 3.2 light years away from us. The present day spaceships would take more than 30000 years to reach there.

Scientists are first trying to find Earth-like planets in the Universe where there is possibility of development of life. Here comes the uniqueness of our Earth. Life can develop in a planet if it lies in the habitable zone of the star. Habitable planets are those that are just at the right distance from their star to have a surface temperature that could sustain liquid water. Earth is at the right distance from the Sun so that we have liquid water here.

Astronomers discovered the first exoplanet around a Sun-like star in 1995. The field of exoplanet discovery and research has been rapidly evolving ever since. At first, astronomers were finding only a few exoplanets each year, but the combination of new cutting-edge facilities focused on exoplanet science with improved detection sensitivity have led to astronomers’ discovering hundreds of exoplanets each year. Scientists are also now able to study  their atmosphere.Today, there are more than 5,000 known exoplanets, ranging from gas giants to small rocky worlds.

But our aim is to find a planet in the habitable zone of its star. Astronomers have now found about a dozen exoplanets that are likely rocky and orbiting within the habitable zones of their respective stars. NASA recently announced the discovery of a new, Earth-sized planet in the habitable zone of a nearby star called TOI-700 for which the prefix TOI means “TESS Object of Interest,” It is only 40% as large as the sun and also has around 40% of Sun’s mass.

TOI-700 first made headlines when NASA announced the discovery of three small planets orbiting the star in early 2020. Using a combination of observations from NASA’s Transiting Exoplanet Surveying Satellite  (TESS) mission and the Spitzer Space Telescope  these planets were discovered by measuring small dips in the amount of light coming from TOI-700.

NASA’s Transiting Exoplanet Survey Satellite (TESS)

The innermost planet, called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than Earth — between the sizes of Earth and Neptune — orbits every 16 days and is likely a gas-dominated world. TOI 700 d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.

Illustration of orbit paths around the star TOI 700

An artist’s view of the newly discovered planet, TOI 700 e.

The TESS observed TOI-700 for another year, from July 2020 through May 2021, and using these observations NASA found the fourth planet, TOI-700 e. TOI-700 e is 95% the size of the Earth and orbits on the inner edge of the star’s habitable zone, between planets c and d. The discovery of this planet makes TOI-700 as one of only a few known systems with two Earth-sized planets orbiting in the habitable zone of their star. The fact that it is relatively close to Earth also makes it one of the most accessible systems in terms of future characterization. TOI-700 e is just over 100 light years from Earth – too far away for humans to visit – but we do know that it is similar in size to the Earth, likely rocky in composition and could potentially support life. Its mass is 0.818 Earths, it takes 27.8 days to complete one orbit of its star, and is 0.134 AU from its star. Its discovery was announced in 2023. The fact that it is relatively close to Earth also makes it one of the most accessible systems in terms of future characterization.