terrestrial planet

 

What exactly is a terrestrial planet?

Terrestrial, or rocky, planets include Earth, Mars, Mercury, and Venus in our solar system. Terrestrial planets are those outsides of our solar system that range in size from half to twice the radius of Earth, and some may be even smaller. Super-Earths are exoplanets that are twice as big as Earth and larger.

Earth-sized and smaller terrestrial planets are rocky worlds made of rock, silicate, water, and/or carbon. It requires more research to discover whether some of these worlds contain atmospheres, oceans, or other indications of habitability. Super-Earths are larger terrestrial exoplanets that are at least twice as massive as Earth.

Learn about some planets that are on Earth.

TRAPPIST-1 e                                     TRAPPIST-1 d

Terrestrial planets typically have a surface made of solid or liquid and a bulk composition that is dominated by rock or iron. Even though these distant worlds may have gaseous atmospheres, that is not what makes them unique.

We've discovered rocky planets in the region of the size of Earth that are sufficiently far from their parent stars to contain liquid water (this is known as the habitable zone). While we can't yet know if these planets actually have atmospheres or seas, these traits can guide us in the right direction. They do not, however, guarantee a habitable world.

Future space telescopes will be able to examine the light coming from some of these planets and look for water or a combination of gases similar to our atmosphere. The surface temperatures will become more clear to us. We'll get closer to discovering a world with detectable evidence of life as we keep crossing off things on the habitability list.

TRAPPIST-1 has seven terrestrial worlds.

The TRAPPIST-1 system, discovered by NASA in 2017, contains the greatest number of Earth-sized planets yet found in a single star's habitable zone. This system of seven rocky planets, all of which have the potential to have liquid water on their surfaces, is an exciting finding in the hunt for extraterrestrial life. Future research on this unusual planetary system might find conditions that are favorable for life.

When the seven planets were examined more closely in February 2018, it was discovered that some of them may contain water in greater quantities than the oceans of Earth, either in the form of liquid water or ice, depending on how close they are to their star. TRAPPIST-1 is now the best-known planetary system outside of our own because of research that more precisely determined each planet's density.

Due to their distance and relative faintness to their host star, it is hard to determine the precise appearance of each planet. Despite having about the same density in our own solar system, the Moon and Mars have quite different seeming surfaces.

Here are the scientists' best hypotheses regarding the planets' appearances based on the information currently available:

The innermost planet, TRAPPIST-1b, is most likely composed of a rocky core that is encircled by an atmosphere that is much thicker than Earth's. Like planet b, TRAPPIST-1c most likely has a rocky interior, although one with a thinner atmosphere. The lightest planet, TRAPPIST-1d, has a mass that is roughly 30% that of the Earth. The presence of a significant atmosphere, ocean, or ice layer, all of which would provide the planet with an "envelope" of volatile elements and make sense for a planet of its density, remains unknown to scientists.

The fact that TRAPPIST-1e is the only planet in the system that is slightly denser than Earth shocked scientists and may indicate that it has a denser iron core than Earth. These two planets are unusual in the system because, like TRAPPIST-1c, they do not necessarily have a dense atmosphere, ocean, or ice layer. Why TRAPPIST-1e is substantially more rock-heavy than the other planets is a mystery. This is the planet that is closest to Earth in terms of size, density, and the quantity of radiation that it receives from its star.

TRAPPIST-1f, g, and h are sufficiently far from the host star for whatever water they may contain to become ice on their surfaces. The heavy Earth chemicals, like carbon dioxide, would not likely be present in their shallow atmospheres.

How many planets that are terrestrial are there?

As we learn more, our understanding may evolve. There are likely to be small, potentially rocky planets in the habitable zones of 20 to 50 percent of the stars in the sky, according to one interpretation of the Kepler Space Telescope's findings. According to more recent evidence, the number is probably lower, possibly between 2 and 12.

When compared to the thousands of exoplanets discovered so far, there appear to be less stony, potentially livable worlds. But that doesn't alter one of the most astounding findings after more than 20 years of observation: planets in the habitable zone are frequent.

More information is required, especially a clearer understanding of the relationship between a planet's size and composition.

Jessie Dotson, an astronomer at NASA's Ames Research Center in California's Silicon Valley, said, "We're still trying to find out how huge a planet can be and still remain rocky." She is also the K2 project scientist for Kepler's extended mission. Even though the spacecraft was retired in 2018, its data is still being used to make discoveries.

A rocky planet with liquid water on its surface may exist around half of the stars with temperatures similar to our Sun, according to a study published in October 2020.

According to findings of research using Kepler data, there are an estimated 300 million of these potentially livable worlds in our galaxy. With four potentially being within 30 light-years of our Sun and the nearest certainly being roughly 20 light-years away, some of these exoplanets might even be our interstellar neighbors.

This study explains the likelihood that these planets contain the components necessary to support life. Astrobiology, the study of the beginnings and future of life in our universe, must include this as a key component. The lead author, Steve Bryson, a researcher at NASA's Ames Research Center in California's Silicon Valley, stated, "Kepler already informed us there were billions of planets, but now we know a large chunk of those planets might be rocky and livable."

The unusual disparity in planet sizes

Scientists have discovered what appears to be an odd gap in the diameters of planets. It is known as the Fulton gap after Benjamin Fulton, the paper's principal author. The Kepler results indicate that planets between 1.5 and 2 times the size of Earth are an uncommon breed. It's possible that this gap represents a crucial turning point in the formation of planets: planets that reach the larger end of the radius gap quickly attract a thick atmosphere of hydrogen and helium gas and balloon up into gaseous planets, whereas planets smaller than the gap are too small to hold such an atmosphere and remain primarily rocky. The cores of Neptune-like worlds that had their atmospheres removed, on the other hand, might be found in the smaller planets that orbit near their sun.

A deeper comprehension of solar system formation will be necessary to explain the Fulton gap.