James Webb Space Telescope First Focus Point Will Be Two Weird Exoplanets

These two planets will serve as a testbed for James Webb space telescope's future in-depth investigations of planets similar to Earth.
james webb telescope

Work on the $10 billion James Webb space telescope is expected to complete its deployment and final testing in June or July and begin its first cycle of observations shortly after. The super-Earth planets 55 Cancri e and LHS 3844 b have recently become the focus of what the Webb telescope will study next.

Although neither of these planets is considered habitable as far as we know, astronomers using the James Webb Space Telescope to hone their skills in observing these two planets.

James Webb Space Telescope Artist Conception
James Webb Space Telescope under CC BY 2.0

The scientific consortium behind the James Webb telescope has set an ambitious goal of studying geology on these minor planets from “50 light-years away.” The work will be a significant test for the new observatory, which is expected to be completed in a few weeks.


James Webb’s deep space position gives it the edge for observing Earth-like planets

Comparatively small size, rocky planets are more challenging to see with present telescope technology than gas giants. The Webb telescope can study these two planets, slightly larger than Earth because of its powerful mirror and deep-space position.

Being adjacent to their star, these two planets set a challenge of relative brightness. Studying them would be extremely difficult with other telescopes; that is why the scientific community is so excited with what the James Webb space telescope will show us in the coming years.

55 Cancri e

55 Cancri e orbits its parent star at a close distance of 1.5 million miles (2.4 million kilometers), about 4% of the distance between Mercury and the sun.

55 Cancri e PIA20068
55 Cancri e by NASA/JPL-Caltech

55 Cancri e possesses blast furnace surface temperatures exceeding the melting point of most types of rocks. 55 Cancri e circles its star just once every 18 hours. Scientists have presumed that Cancri e is tidally locked to the star, which means that one side always faces the searing sun, while studies from NASA’s Spitzer Space Telescope indicate that the hottest zone could be slightly offset.

According to scientists, the offset heat could be caused by a thick atmosphere that can transfer heat around the globe or by lava raining at night, which removes heat from the atmosphere. (Nighttime lava also suggests a day-night cycle, which could be owing to a 3:2 resonance, or three spins for every two orbits, as seen on Mercury in our own solar system.)

Two teams will test these hypotheses: one, led by Renyu Hu of NASA’s Jet Propulsion Laboratory, will look for traces of an atmosphere in the planet’s thermal emission, while the other, led by Alexis Brandeker of Stockholm University, will study heat emittance from 55 Cancri e’s illuminated side.


LHS 3844 b 

LHS 3844 b is also close to its star, rotating once every 11 hours around its parent star. The parent star of LHS 3844 b is smaller and cooler than 55 Cancri e. As a result, LHS 3844 b’s surface is anticipated to be significantly cooler. Spitzer’s observations (infrared space telescope) have revealed that the planet has no significant atmosphere.

1024px PIA23130 Exoplanet LHS3844b ArtistConcept 20190819
Exoplanet-LHS3844b by NASA/JPL

A team at the Max Planck Institute for Astronomy led by astronomer Laura Kreidberg seeks to catch a surface signal using spectroscopy. To examine if a surface composition can be identified, thermal emission spectrums from the planet’s daylight side will be compared to known rocks such as basalt and granite. Light of different wavelengths denotes different elements.

Final preparations

Before astronomers study LHS 3844 b and 55 Cancri e, some evaluations are needed on mirror and instrument alignment. The James Webb telescope must complete final commissioning procedures such as tracking solar system targets and changing between hotter and cooler attitudes. 


What do scientists hope to learn?

Scientists hope that studying these two planets will give them new insights into what the early Earth would have been like when it was hot like these planets are today and learning about planets in general.

Feature image credit: Artist’s impression of 55 Cancri e by ESA/Hubble, M. Kornmesser under CC BY 4.0