TRAPPIST-1f, also designated as 2MASS J23062928-0502285 f, is an exoplanet, likely

rocky ''Rocky'' is a 1976 American sports drama film directed by John G. Avildsen and written by and starring Sylvester Stallone. It is the first installment in the ''Rocky'' franchise and stars Talia Shire, Burt Young, Carl Weathers, and Burge ...

, orbiting within the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kast ...

around the ultracool dwarf star TRAPPIST-1, located away from Earth in the constellation of

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainme ...

. The exoplanet was found by using the

transit method Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...

, in which the dimming effect that a planet causes as it crosses in front of its star is measured. It was one of four new exoplanets to be discovered orbiting the star in 2017 using observations from the Spitzer Space Telescope. The planet is likely

tidally locked Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked bo ...

, and has been depicted as an eyeball planet in artistic impressions by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

Physical characteristics

Mass, radius, and temperature

TRAPPIST-1f is an Earth-sized exoplanet, meaning it has a radius close to that of Earth. It has an

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...

of . It has a radius of and a mass of . It was initially estimated to have a much lower mass, and thus a low density of and a

surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

around (62% of Earth's value). This suggested a large amount of

volatiles Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances. On planet Earth, the term ...

, with a 2017 study suggesting that a water ocean may comprise as much as 20% of the planet's mass, increasing the temperature at the bottom of such an ocean to above . However, refined density estimates show that TRAPPIST-1f, like other planets in the system, is only slightly less dense than Earth, consistent with a rocky composition.

Atmosphere

According to simulations of magma ocean-atmosphere interaction, TRAPPIST-1f is likely to retain a fraction of primordial steam atmosphere during the initial stages of evolution, and therefore today is likely to possess a thick ocean covered by atmosphere rich in abiotic oxygen. Helium emission from TRAPPIST-1f (and planets b and e) has not been detected as of 2022.

Host star

The planet orbits an ( M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 and a radius of 0.11 . It has a temperature of 2550 K and is at least 7-8 billion years old. In comparison, the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ( e/H of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerably less metal content than the Sun; on the other hand, metal-rich stars are also more likely to have planets than metal-poor ones. Its luminosity () is 0.05% of that of the Sun. The star's

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.

Orbit

TRAPPIST-1f orbits its host star with an orbital period of about 9.206 days and an orbital radius of about 0.037 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).

Habitability

The exoplanet was announced to be either orbiting within or slightly outside of the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. On 31 August 2017, astronomers at the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

reported the first evidence of possible water content on the TRAPPIST-1 exoplanets. TRAPPIST-1f has a radius about the same as Earth, at around 1.045 , but was initially thought to have only about two thirds of Earth's mass, at around 0.68 . So, it was considered somewhat unlikely to be a fully rocky planet, and extremely unlikely to be an Earth-like one, that is rocky with a large iron core but without a thick hydrogen-helium atmosphere enveloping the planet. Simulations in 2017 suggested the planet is approximately 20% water by composition, much higher than that of Earth. With such a massive water envelope, the pressure and temperature will be high enough to keep the water in a gaseous state and any liquid water will only exist as clouds near the top of TRAPPIST-1f's atmosphere. Based on this study, TRAPPIST-1f is therefore likely to be no more habitable than any other

ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary scienc ...

with water clouds in its atmosphere. However, refined estimates show that TRAPPIST-1f has about the same mass as Earth, and like other planets in the system, is only slightly less dense than Earth, consistent with a rocky composition. Its host star is a

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...

ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

s and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live. Because of this ability to live for long periods of time, it is likely TRAPPIST-1 will be one of the last remaining stars when the Universe is much older than it is now, when the gas needed to form new stars will be exhausted, and the remaining ones begin to die off. The planet is very likely tidally locked, with one hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. However, between these two intense areas, there would be a sliver of moderate temperature – called the terminator line, where the temperatures may be suitable (about ) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

References

External links

NASA Briefing on the Discovery of TRAPPIST-1's 7 Planets
{{DEFAULTSORT:TRAPPIST-1f Exoplanets discovered in 2017 Near-Earth-sized exoplanets Near-Earth-sized exoplanets in the habitable zone Transiting exoplanets TRAPPIST-1 Aquarius (constellation)