Chapter 1: Introduction to GJ 357 d

The Transiting Exoplanet Survey Satellite (TESS) has made a groundbreaking discovery by identifying its first super-Earth, GJ 357 d, situated near our solar system. This intriguing planet resides within the habitable zone of its star, where conditions may allow water to exist in liquid form, potentially creating oceans.

The star GJ 357, an M-type star, is significantly smaller and cooler than our Sun, being only one-third its size and mass. Located approximately 31 light years away in the direction of the constellation Hydra, this system hosts at least three known planets.

“This is thrilling; it marks humanity’s first nearby super-Earth that could possibly support life—thanks to TESS, our small but impactful mission,” stated Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University.

Astronomers using NASA’s TESS observatory detected a recurring dimming of light from GJ 357, first observed in February 2019, occurring every 3.9 days. This observation led to the identification of three planets in the system, with the outermost potentially being habitable.

“In a sense, these planets were hidden within data collected from various observatories over many years. It was TESS that guided us to an intriguing star where we could uncover them,” explained Rafael Luque, a doctoral student at the Institute of Astrophysics of the Canary Islands (IAC).

Section 1.1: Understanding the System's Composition

The innermost exoplanet, GJ 357 b, is only 22 percent larger than Earth. However, its proximity—just nine percent of the distance between the Sun and Mercury—results in extreme temperatures. Even without an atmosphere, its surface temperature would reach 254 degrees Celsius (490 Fahrenheit), making it uninhabitable.

The middle planet, GJ 357 c, orbits its star every 9.1 days and remains at a distance double that of GJ 357 b. Despite this distance, temperatures would still soar to 127 C (260 F) without an atmosphere, rendering it lifeless.

If GJ 357 d is primarily rocky, it would be roughly twice the size of Earth and possess a mass over six times greater than our planet. It completes an orbit around its star every 55.7 days, receiving sunlight similar to what Mars gets from our Sun. Without an atmosphere, this planet would have a chilling temperature of -53 C (-64 F).

“GJ 357 d is located near the outer edge of its star's habitable zone. If this planet possesses a thick atmosphere, future studies may reveal that it could retain enough heat to support liquid water on its surface,” noted Diana Kossakowski from the Max Planck Institute for Astronomy in Heidelberg, Germany.

“A time will come when men will stretch out their eyes. They should see planets like our Earth.”

? Christopher Wren, Scientist, 1632–1723

Section 1.2: Methods of Discovery

Only GJ 357 b was found using the transit method, as it passed between its star and our observational line. The other two planets were detected through their gravitational effects on the star, a technique known as the radial velocity method.

To date, around 200 exoplanets orbiting 100 M-dwarf stars have been identified in our local stellar neighborhood. However, only eleven M dwarf systems have been confirmed using both the transit and radial velocity methods, allowing researchers to calculate their density based on radius and mass.

Chapter 2: The Future of Exoplanet Exploration

The TESS spacecraft was engineered to survey the skies, identifying planets that transit in front of their stars. Since its launch in April 2018, TESS has confirmed 24 planets and identified 993 candidate worlds for further investigation. Over its two-year mission, TESS aims to discover around 20,000 new planets, significantly expanding our knowledge beyond the 4,000 exoplanets already known.

Data from TESS was integrated with observations from various instruments dating back to 1998 to confirm the findings. Astronomers are eager to explore the atmospheres of the planets within the GJ 357 system using the forthcoming Extremely Large Telescopes (ELT) and the James Webb Space Telescope, which is set to launch in March 2021. This research could provide insights into the possibility of life, even at a primitive level, on this promising world.

Did you enjoy this article? Subscribe to The Cosmic Companion Newsletter!

The second video, titled "TESS Discovers a Remarkable Earth Like Planet In The Habitable Zone," delves into TESS's findings of potentially habitable planets, highlighting the significance of this research in the search for extraterrestrial life.