Kepler-138c and Kepler-138d

Why in news?

• A team of researchers has announced that two previously discovered exoplanets Kepler-138c and Kepler-138d are “water worlds” which means they are primarily made of water.

Background:

• In 2014, astronomers discovered three exoplanets orbiting Kepler-138, a star 218 light years from Earth.
• They observed two of these exoplanets Kepler-138c and Kepler-138d with Hubble and the retired Spitzer space telescopes.

Key findings of the researchers:

• The unique factor of the two exoplanets was that watery liquid makes up a large part of their composition.
• Notably, water on these exoplanets wasn’t detected directly. Researchers compared the sizes and masses of the planets to conclude that a significant fraction of their volume — up to half of it — should be made of materials that are lighter than rock but heavier than hydrogen or helium — and water is the most common material that fits that criteria.
• The closest comparisons to these water worlds are Europa and Enceladus — icy moons orbiting Jupiter and Saturn, respectively — but because Kepler-138 c and Kepler-138 d are so much closer to their star, their water would not be frozen.

PRACTICE QUESTION:

Kepler-138c and Kepler-138d, recently seen in news are:

(a) Exoplanets

(b) Comets

(c) Meteoroid

(d) Black holes

Answer