FYI.

This story is over 5 years old.

Tech

The Newly Discovered Waterworld is a Celestial Jacuzzi

To make planetary classification harder, just add water.

Generally speaking, there are three types of planets in our Solar System: the rocky, terrestrial Mercury, Venus, Earth, and Mars; the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune. Pluto is a dwarf planet, a separate category of bodies that are either too small or irregular to fit in with the larger bodies.

Classifying planets gets a lot harder when you get to other stars. Exoplanets come in a wider variety, including lava worlds and hot Jupiters. But the latest planetary find is something astronomers have never seen before—a water world.

Advertisement

The planet, which goes by its astronomical designation of GJ1214b, was discovered in 2009 by the ground-based MEarth Project (pronounced "mirth"). It's a super Earth; its diameter is about 2.7 times that of Earth and it's nearly 7 times the mass of our planet. It orbits an average of 3.8 million miles away from its star, a red dwarf some 40 light years away, and its year is roughly 30 hours long. With this data, GJ1214b's discoverers have determined that the planet has a surface temperature of around 450 degrees Fahrenheit.

In 2010, astronomers dug deeper into this super Earth discovery, measuring the planet's atmosphere with the Hubble space telescope. They found the planet was mainly composed of water, but it wasn't immediately clear whether it had large oceans or a water-rich atmospheric haze.

So they went back to Hubble, this time using the telescope's Wide Field Camera 3 (WFC3). The high resolution camera, which was installed in 2009, uses two channels to gather light in two wavelengths to create a complete image. It can function in the near-infrared, visible, and near-ultraviolet portions of the electromagnetic spectrum.

Hubble watched GJ1214b as it crossed in front of its star. Every gas absorbs light in a known way, so astronomers can look at the light passing through a planet's atmosphere to determine what it's made of. To study GJ1214b, astronomers focussed on the infrared color of the sunset. Haze is more transparent to infrared light than it is to visible light, so data in this spectrum helped them determine where the observed water was coming from. They found that GJ1214b's specturm was almost entirely featureless over a wide range of wavelengths. Hubble found that the planet's atmosphere is likely dense and made up of water vapor. It's probably a very steamy planet.

Taking this information about the atmosphere in combination with the planet's known size and density, astronomers have been able to make a fair guess about its composition. GJ1214b has much more water and much less rock than Earth, and its internal structure is likely very different from Earth's.

The leading theory is that GJ1214b formed farther out from its star where water ice was plentiful, then migrated inward early in its system's history. In the process, it would have passed through the star's habitable zone but it's not known how long it stayed there.

Connections: