Mysterious Worlds Beyond Our Own

Tzvetelina Dimitrova

On Earth, we often find ourselves looking

out into the night sky wondering at the

mysteries that lie beyond the solar system

we call home. What are the planets like

beyond our planetary neighborhood? Could

their landscapes resemble our own? Or

could they hold mysteries beyond our

modern comprehension? On exploring the

topic of mysterious exoplanets, TRAPPIST-

1 is certainly the right place to start.

TRAPPIST-1 is a planetary system located

at a distance of 39 light years (in miles)

from the Sun, within the constellation

Aquarius [1]. The planetary system consists

of at least seven planets (Figure 1), which

orbit about an ultra-cool red dwarf star that

is 12 times less massive than the Sun, and

slightly larger than Jupiter [1]. This system

is of importance in the exoplanet field,

because of its central dwarf star. Planets that

orbit about ultra-cool red dwarfs tend to

have similar planetary characteristics to

earth in several different aspects. The

discovery of seven temperate terrestrial

planets is a significant discovery because

this is the greatest number of planets

detected in any system. Three of these

newly discovered planets are considered to

lie within the habitable zone of the star.

Timeline

Although the central TRAPPIST-1 star

was discovered in 1999 during the Two

Micron All Sky Survey(2MASS) [2], the

detection of a planetary system is a

relatively recent development. In May of

2016, Michael Gillon and his team at the

University of Liege in Belgium published

findings of three Earth-sized planets

orbiting the star. They used the method of

transit photometry, with the Transiting

Planets and Planetesimals Small Telescope

(TRAPPIST) at the La Silla Observatory

in Chile[3]. On June 6th, the first transit of

the planet TRAPPIST-1d was detected!

Not long after, on October 11th, the first

Figure 1 Trappist-1 exoplanetary system NASA/JPL-Caltech image.

transit of planet 1h was observed as well.

Almost a year later, on August 31st 2017,

exciting news broke! A scientific paper

reported Ultraviolet observations, which led

to the suggestion that the outer planets

might host water.

Following these discoveries,

multiple series of scientific papers have

been published on the planets. These new

papers outlined the more recently

discovered characteristics of the system. At

this point, a record-breaking total of seven

planets had been observed. All these seven

planets were discovered using the transit

method, during which the recorded

brightness of a host star is observed for

periodic dips suggesting an orbiting body

(Figure 2). Following these discoveries, the

next course of action called for

investigations into the atmospheric

conditions of the planets, as well as their

habitability and likelihood of liquid water.

Now let us journey far beyond our bounds

on earth, and dive into the most notable

properties of the TRAPPIST-1 planetary

system! The innermost planet,

TRAPPIST-1b, is a rocky planet sharing

some characteristics of our solar systems

very own planet Venus as its atmosphere

is incredibly hot and thick. TRAPPIST 1-

b’s size is comparable to that of Earth,

although its atmosphere has a much

greater reach, and its density is relatively

low. TRAPPIST-1c is the third largest

planet of the system, and it is also the most

massive. Similar to planet 1b in

atmosphere and composition, the most

intriguing fact about this planet is the

proximity of its orbit around the host star,

which causes a year on this planet to last a

mere 58 hours! TRAPPIST-1d is the

smallest planet and falls into the inner

edge of the habitable zone of the red dwarf

star, although recent studies conducted by

the University of Washington suggest it to

be uninhabitable and Venus like [4].

TRAPPIST-1e is a relatively Earth like

exoplanet, with a comparable size, mass,

temperature, and, stellar flux to that of

Earth. Out of all of the planets in the

system, TRAPPIST-1e has the most

potential to be a habitable ocean planet,

and for this fact has been deemed the most

Figure 2 - Spitzer Space Telescope transit data of

TRAPPIST-1. Credit: ESO/M. Gillon et al.TRAPPIST-1

worthy of further study (Figure 3). Further

out into the habitable zone, TRAPPIST-1f is

a partially rocky planet theorized to host

liquid water oceans on its surface under the

right atmospheric conditions. TRAPPIST-1g

is thought to be just barely within, or just

barely outside of the habitable zone, and is

also thought to be a likely candidate to host

some form of water. The last and outermost

planet of the system is TRAPPIST-1h.

Although not significantly smaller than

earth, it has a relatively low density which

suggests the presence of water, and or ice.

At its orbital distance from its host star, this

planet is within the frost line, the point at

which common planetary compounds are

thought to freeze [5]. Regardless of whether

or not the planets of the TRAPPIST-1

system prove to be habitable to human life,

they are surely the first of their kind to be

discovered, and promise to be a hub for

fascinating future research!

Figure 3 "Planet hop from TRAPPIST-1e - Voted best 'hab zone'

vacation within 12 parsecs of Earth" NASA Exoplanets Exploration

Program's Exoplanet Travel Bureau poster

SourcesCited[1]Gillon,AmauryTriaudMichael.“1.”TRAPPIST,Retrieved

6022020,fromwww.trappist.one/.

[2]Gizis,JohnE.;Monet,DavidG.;Reid,I.Neill;Kirkpatrick,

J. Davy; Liebert, James; Williams, Rik J. (2000). "New

Neighbors from 2MASS: Activity and Kinematics at the

Bottom of the Main Sequence". The Astronomical Journal.

120 (2): 1085–1095. arXiv:astro-ph/0004361.

Bibcode:2000AJ....120.1085G.doi:10.1086/301456.

[3] Gillon, M., Jehin, E., Lederer, S. et al. Temperate Earth-

sized planets transiting a nearby ultracool dwarf star.

Nature 533, 221–224 (2016).

https://doi.org/10.1038/nature17448

[4] Kelley, P. (2018, November 20). Study brings new

climatemodelsof small starTRAPPIST1’sseven intriguing

worlds. Retrieved from

https://www.washington.edu/news/2018/11/20/study-

brings-new-climate-models-of-small-star-trappist-1s-seven-

intriguing-worlds/

[5]Kelley,P. (2018,November20).Studybringsnewclimate

models of small star TRAPPIST 1’s seven intriguing worlds.

Retrieved from

https://www.washington.edu/news/2018/11/20/study-

brings-new-climate-models-of-small-star-trappist-1s-seven-

intriguing-worlds/