Super-Earth in Habitable Zone

The search for a “second Earth” has taken a significant leap forward. Astronomers have recently identified fascinating worlds that are not only similar in size to our own planet but also reside in the specific region around their stars where liquid water could exist. The discovery of planets like TOI-715 b and Gliese 12 b marks a pivotal moment in exoplanet research, moving us from finding gas giants to identifying rocky worlds that might support life.

The Discovery of TOI-715 b

In early 2024, an international team of scientists led by Georgina Dransfield of the University of Birmingham announced the discovery of a “Super-Earth” named TOI-715 b. This planet was found using NASA’s Transiting Exoplanet Survey Satellite (TESS), a space telescope specifically designed to find planets orbiting the brightest stars in the sky.

This discovery is particularly exciting for several reasons:

  • Location: It orbits within the “conservative habitable zone” of its parent star. This is a specific range where conditions are most likely to allow liquid water to pool on the surface.
  • Size: It is approximately 1.55 times the width of Earth. This classifies it as a Super-Earth, meaning it is likely rocky rather than gaseous.
  • Distance: The system is located about 137 light-years away from Earth. While this is too far for human travel, it is close enough for our most powerful telescopes to study its atmosphere.

Understanding the "Goldilocks Zone"

The term “habitable zone” refers to the distance from a star where it is neither too hot nor too cold for liquid water to exist. It is often called the Goldilocks zone.

TOI-715 b orbits a red dwarf star. Red dwarfs are smaller and cooler than our Sun. Because the star is cooler, the habitable zone is much closer to the star itself. Consequently, TOI-715 b completes a full orbit—a year on that planet—in just 19 days.

While being this close to a star usually presents risks like dangerous solar flares, the star TOI-715 appears to be relatively quiet. This lack of intense magnetic activity increases the chances that the planet has retained an atmosphere over billions of years.

Gliese 12 b: The Nearest Temperate World

Following closely on the heels of the TOI-715 b announcement, astronomers revealed another major find in May 2024: Gliese 12 b. This planet offers a different perspective on habitability and is located significantly closer to us, at just 40 light-years away in the constellation Pisces.

Gliese 12 b is notable for its similarity to Earth and Venus in size. Unlike TOI-715 b, which is a Super-Earth, Gliese 12 b is almost the exact same size as Venus, making it slightly smaller than Earth.

Key Statistics for Gliese 12 b:

  • Surface Temperature: Scientists estimate the surface temperature is around 42 degrees Celsius (107 degrees Fahrenheit). This is remarkably temperate for an exoplanet and suggests it might not have suffered the same runaway greenhouse effect as Venus.
  • Star Type: It orbits a cool red dwarf star called Gliese 12.
  • Orbit: It completes a trip around its star every 12.8 days.

The Next Step: Investigating Atmospheres

Finding these planets is only the first step. The critical question remains: do they have atmospheres?

A planet in the habitable zone without an atmosphere is essentially a dead rock. To answer this, astronomers are turning to the James Webb Space Telescope (JWST). JWST is the only telescope currently capable of performing “transmission spectroscopy” on planets of this size.

Here is how the process works:

  1. Transit: The telescope waits for the planet to pass in front of its star.
  2. Filtration: As starlight passes through the planet’s edges, it filters through the atmosphere (if one exists).
  3. Analysis: The gases in the atmosphere absorb specific colors of light. By analyzing the missing light, scientists can identify chemical fingerprints.

For TOI-715 b and Gliese 12 b, scientists are looking for signatures of water vapor, methane, carbon dioxide, and potentially oxygen. If JWST detects these gases, it would be the strongest evidence yet of a habitable environment beyond our solar system.

Why Super-Earths Matter

Super-Earths are a class of planets with masses higher than Earth’s but lower than ice giants like Neptune. Interestingly, while Super-Earths appear to be the most common type of planet in our galaxy, our own solar system does not have one.

We have small rocky planets (Earth, Mars) and gas giants (Jupiter, Saturn), but nothing in between. Studying planets like TOI-715 b helps scientists understand how these common worlds form and whether they are generally more or less hospitable to life than Earth-sized worlds.

The discovery of these planets confirms that rocky worlds in habitable zones are not rare anomalies. They are likely abundant throughout the Milky Way, waiting for our technology to catch up and reveal their secrets.

Frequently Asked Questions

Does TOI-715 b have water? We do not know yet. Being in the habitable zone only means that water could exist physically, not that it does. The James Webb Space Telescope is required to detect actual water vapor in the atmosphere.

Can we travel to these new planets? No. TOI-715 b is 137 light-years away. Even traveling at the speed of the fastest spacecraft ever built (the Parker Solar Probe), it would take hundreds of thousands of years to reach it.

Is there life on these planets? There is no evidence of life yet. Finding a planet in the habitable zone is a prerequisite for finding life as we know it, but it is not proof. Scientists look for “biosignatures,” which are combinations of gases (like methane and oxygen together) that usually require biological processes to maintain.

Why are red dwarf stars important for finding planets? Red dwarfs are the most common stars in the galaxy. They are also small and dim. This makes it easier to detect planets orbiting them because the planet blocks a larger percentage of the star’s light during transit compared to a bright, massive star like our Sun.