TRAPPIST-1e has an Iron Core

A new study published on April 26, 2018, suggests that TRAPPIST-1e, an exoplanet orbiting the red dwarf star TRAPPIST-1, has a large iron core. This could mean that the planet TRAPPIST-1e may have a protective magnetosphereNotes 1 like we have here on Earth.

In their study, Suissa and Kipping took advantage of recent studies that measured the planetary masses of TRAPPIST-1 system with precisions ranging from 5% to 12%. TRAPPIST-1e, the fourth planet of the system, has a density of 5.6 g/cm3, which is slightly higher than that of Earth (5.51 g/cm3). Using the original maximum formulation for planets g and h, the researchers were able to derive a minimum and maximum core size for each planet (using the original maximum formulation for planets g and h). They found that the minimum core size is consistent with zero for all of the planets except TRAPPIST-1e.

TRAPPIST-1e “has a large iron core”

In particular, for planet c, Suissa and Kipping found that the probability of an iron core is modest at 57%. According to the researchers, thus ambiguity remains regarding TRAPPIST-1c’s interior. For planet Trappist-1e, however, 99.3% of the posterior samples are consistent with a silicate-iron model indicating strong evidence for an iron core, researchers conclude. They published their findings with the title of “TRAPPIST-1e Has a Large Iron Core”.

TRAPPIST-1e artist conception
An artis’s conception of TRAPPIST-1e, an exoplanet orbiting its star TRAPPIST-1 in habitable zone. TRAPPIST-1, also designated as 2MASS J23062928-0502285, is an ultra-cool red dwarf star located 39.6 light-years (12.1 pc) from the Sun. It is slightly larger but much more massive than the planet Jupiter. In this artis’s depiction, TRAPPIST-1e shown covered in water with ice caps on the night side (all seven planets of the TRAPPIST-1 system are likely to be tidally locked, which means one side of each planet permanently facing the star, making the development of life there “much more challenging”). TRAPPIST-1e has a slightly higher density than Earth, indicating a terrestrial rock and iron composition.

On February 22, 2017, NASA has announced that seven Earth-sized planets have been observed by NASA’s Spitzer Space Telescope around ultra-cool red dwarf star TRAPPIST-1, with three of these planets are firmly in the habitable zone. Further observations revealed that the system contains water, and then the Hubble Space Telescope has revealed that the planets also have athmospheres.

These may seem like good news for the search for extraterrestrial life, but, all seven planets of the TRAPPIST-1 system are likely to be tidally locked, which means one side of each planet permanently facing the star, making the development of life there “much more challenging”.

TRAPPIST-1 system compared to Earth (February 2018)
TRAPPIST-1 system compared to Earth (February 2018). TRAPPIST-1 is an ultra-cool dwarf star, which is only about 9 percent as massive as our Sun. It is slightly larger than the planet Jupiter in size, but has much more mass. It is located 39.6 light-years (12.1 pc) from the Sun in the constellation Aquarius. It was discovered in 1999 and astronomers first discovered three Earth-sized planets orbiting the dwarf star in 2015. On 22 February 2017, astronomers announced four additional exoplanets around TRAPPIST-1, and three of them were in the habitable zone

Why having an iron core matters?

With having an iron core, Trappist-1e is likely to have a magnetosphere. Planets having active magnetospheres, like the Earth, are capable of mitigating or blocking the effects of solar radiation or cosmic radiation, that also protects all living organisms from potentially detrimental and dangerous consequences.

Without the magnetosphere, for example, the Earth’s atmosphere could be stripped by the solar particles, exactly like it happened on Mars when it lost its own magnetic field. By contrast, Earth’s magnetosphere seems to have kept our atmosphere protected.

Mars - Valles Marineris Hemisphere Enhanced
Mars may once have been more hospitable to life than it is now. Scientists think the magnetosphere of Mars collapsed around 3.7 billion years ago, and it eventually lost its atmosphere. Now, Mars has a very thin atmosphere: the atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi; 6.0 mbar), about only 0.6% of Earth’s mean sea level pressure of 101.3 kilopascals (14.69 psi; 1.013 bar). Photo: NASA

Watch: TRAPPIST-1 Planets Flyaround Animation published by NASA Spitzer channel

This video depicts artist’s concepts of each of the seven planets orbiting TRAPPIST-1. Over 21 days, NASA’s Spitzer Space Telescope measured the drop in light as each planet passed in front of the star. Spitzer was able to identify a total of seven rocky worlds, including three in the habitable zone where life is possible. The study established the planets’ size, distance from their sun and, for some of them, their approximate mass and density. It also established that some, if not all, these planets are tidally locked, meaning one face of the planet permanently faces their sun.

The planets appear in the order of innermost to outermost planets. TRAPPIST-1b, closest to the star, was modeled on Jupiter’s moon Io, which has volcanic features due to strong gravitational tugs. TRAPPIST-1c is shown as a rocky, warm world with a small ice cap on the side that never faces the star. TRAPPIST-1d is rocky and has water only in a thin band along the terminator, dividing the day side and night side.

TRAPPIST-1e and TRAPPIST-1f are both shown covered in water, but with progressively larger ice caps on the night side. TRAPPIST-1e has also a slightly higher density than Earth, indicating a terrestrial rock and iron composition. TRAPPIST-1g is portrayed with an atmosphere like Neptune’s, although it is still a rocky world. The farthest planet, TRAPPIST-1h, is shown as covered in ice, similar to Jupiter’s icy moon Europa.

The background stars are what you would see if you were in the TRAPPIST-1 system. Orion passes behind the planets, recognizable but distorted from what we’re familiar with, in addition to Taurus and Pleiades.

Notes

  1. A magnetosphere is the region of space surrounding an astronomical object in which charged particles are manipulated or affected by that object’s magnetic field. It is created by planets having active hot iron and nickel or metallic cores, whose motion generated a planetary magnetic field, but such fields can also occur in stars by the interactions of plasma. Planets having active magnetospheres, like the Earth, are capable of mitigating or blocking the effects of solar radiation or cosmic radiation, that also protects all living organisms from potentially detrimental and dangerous consequences.

Sources

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