TRAPPIST-1f, also known as 2MASS J23062928-0502285 f, is a terrestrial extrasolar planet orbiting around the ultra-cold dwarf star TRAPPIST-1, located approximately 39 light-years (12 parsecs) away from Earth in the constellation Aquarius. It is likely rocky, but under a massive water-steam gaseous envelope at very high pressure and temperature
It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope.
Characteristics[]
Mass, radius, and temperature[]
TRAPPIST-1f is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 219 K (-54 °C; -65 °F), which increases to above 1,400 K (1,130 °C; 2,060 °F) if the warming of its likely very dense atmosphere is taken into account. It has a radius of 1.045 ± 0.038 Earth radii (R⊕) and a mass of 0.68 ± 0.18 Earth mass (M⊕), giving it a density of 3.3 ± 0.9 g/cm3. These values suggest surface gravity around 6.1 m/s2 (62% of Earth value).
Host star[]
The planet orbits an (late M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.089 Solar mass (M☉) and a radius of 0.121 Solar radius (R☉). It has a temperature of 2516 K and is anywhere between 3 and 8 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is metal-rich, with a metallicity ([Fe/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. Its luminosity (L☉) is 0.0522% of that of the Sun.
The star's apparent magnitude, 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[]
Artist's impression of the surface of TRAPPIST-1f, depicting a liquid water ocean on its surface. The parent star and neighbouring planets are also illustrated.
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 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 R⊕, but only about two thirds of Earth's mass, at around 0.68 M⊕. So, it is 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 strongly suggest the planet is approximately 20% water by composition. 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. Trappist-1f is therefore likely to be no more habitable than any other gas or ice-giant with water clouds in its atmosphere.
Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs 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 habitability – called the terminator line, where the temperatures may be suitable (about 273 K or 0 °C or 32 °F) 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.