Kiel (UK), After the formation of our solar system 4.6 billion years ago, tiny particles of dust and ice swirled in space, the remnants of the Sun’s formation. Over time, they collided and stuck to each other. As they grew in size, gravity helped them collide. One such rock evolved into the earth on which we live.
We now believe that most of the stars visible in the night sky are also orbited by their own planets. Astronomers have already found more than a thousand gas-major planets – large, gaseous bodies the same size as Jupiter. The focus is now on the search for rocky, Earth-sized planets. We expect these to be equally abundant, but being so small, they are hard to find.
A new paper published in the journal Science documents the latest discovery of a minor planet, given the catalog number GJ 367b. This exoplanet was discovered by a team led by Dr. Christine Lamm from the Institute of Planetary Research at the German Aerospace Center, of which I was a member.
Team members saw the first signs of GJ 367b in data from NASA’s Transiting Exoplanet Survey Satellite, or TESS. One of the millions of stars being monitored by this satellite showed a small but periodic drop in its brightness. This is a signal of a planet passing in front of its star (called a “transit”), which blocks some of the star’s light. Its brightness drop was only 0.03% deep, so little that it is difficult to detect. This means that it should be comparatively the size of the Earth.
Lam also wanted to know about the mass of the planet. To do this, his team decided to observe every possible chance of seeing this star with the High Accuracy Radial Velocity Planet Searcher, or HARPS. It is an instrument attached to the 3.6 meter telescope at the European Southern Observatory in Chile. It was specifically designed to detect planets by detecting slight changes in the wavelength of light of the associated star due to the gravitational pull of the planet. It took more than 100 observations to detect that change, which means that GJ 367 b, in addition to being smaller, must also have a lower mass.
Eventually, the researchers explained it with numbers, observing with Harps. According to this, the radius of GJ 367 b is 72% (to an accuracy of 7%) of Earth’s radius, and its mass is 55% (to an accuracy of 14%) of Earth’s mass. Measurements tell us that this planet is denser than Earth. While Earth has an iron core surrounded by a rocky mantle, the planet is so dense that it must be almost entirely of iron, which makes it similar to Mercury.
Mercury orbits the Sun every 88 days. Due to the scorching sun, its surface keeps burning. Its surface heats up to 430 degrees “in the daytime”. GJ 367B is even hotter. Recurrent transit fallacy tells us that it orbits its star in just eight hours. Being so close, during the day it heats up to 1,400 degrees like a furnace, hot enough to melt even a rock.
So how did it go? It is possible that GJ 367b was once a giant planet like Neptune, which was covered with gases. It is estimated that over time, that gaseous envelope dissipated and the blank surface we see today emerged. Or perhaps, as it formed, collisions with other proto-planets (in the process of planetary formation) removed a mantle of rock, leaving only an iron core.
GJ 367b is so hot that it is almost impossible for life to exist on it. But it is one of the very few rocky, Earth-sized planets that astronomers have discovered so far. Its discovery suggests that we can find Earth-sized planets around other stars and measure their properties. The task now is to find them in the “habitable zone” on the far side of their stars, where surface temperatures will allow water to exist as a liquid.
This is difficult. The further a planet is from its star, the less likely it is to be seen crossing the star, and the longer the time between transits, the harder it is to detect them. Additionally, as we orbit further, the gravitational effect on the host star is reduced, making the signal harder to detect.
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