Here’s what we know for sure about the planet K2-18b. It’s about 125 light-years away. It’s bigger and heavier than Earth. It orbits a cool, faint star once every 33 days. It receives about the same amount of energy from its star as Earth gets from the Sun. And it has an atmosphere.

After that, things get muddled. Astronomers aren’t sure about the structure of the planet or the make-up of its atmosphere. And ideas about whether it might be habitable are all over the place. The confusion highlights the challenges of studying planets in other star systems.

K2-18b passes in front of its star on every orbit. And as it does so, the chemical “fingerprints” of its atmosphere are added to the starlight. Substracting the starlight provides a profile of the atmosphere. But the profile is hard to read. Many of the fingerprints are subtle, and can be produced by different compounds.

Earlier this year, a team announced the discovery of compounds in the atmosphere that could be produced by microscopic life. Follow-up studies by other groups contradicted that finding. But the original study team has stuck by its conclusions. So it’ll take a lot more work to know for sure what’s going on at K2-18b.

The K2-18 system is in Leo, which climbs into good view after midnight. K2-18 is to the right of Denebola, the star that marks the lion’s tail. But it’s too faint to see without a telescope.

Script by Damond Benningfield

For stars that are similar to the Sun, the end comes in stages. And each stage is triggered by changes in the star’s core. One star that’s going through those changes is Diphda, the brightest star of Cetus, the sea monster.

The star is several hundred million years old – billions of years younger than the Sun. For most of its life, it “fused” hydrogen atoms in its core to make helium. When the hydrogen was gone, it began fusing hydrogen in a shell around the core. That made the star puff up, so it was classified as a red giant.

Now, it’s finished off the shell, so it’s fusing the helium in the core to make carbon and oxygen. This phase is generally lumped into the red-giant category. Technically, though, it has its own name: the red clump.

In a hundred million years or so, Diphda will have used up all the helium. The star isn’t massive enough to fuse the carbon and oxygen to make heavier elements. Without that energy, the core will collapse to about the size of Earth. It’ll be extremely hot, though, so it’ll blow away Diphda’s outer layers. For a while, the star will enter one more phase: a planetary nebula – a colorful cloud of gas and dust.

When the cloud disperses, only the dead core will remain: a white dwarf – the hot but tiny remnant of a star.

Cetus spreads across the southeastern quadrant of the sky at nightfall. Diphda is near its lower right corner, roughly a third of the way up the sky.

Script by Damond Benningfield

People collect all kinds of things, from baseball cards to Persian rugs. Over the past 40 years, some NASA aircraft have collected dust – grains of dust from beyond Earth. Many of the collection efforts have taken place during meteor showers. That’s included the Geminid shower, which is at its peak tonight.

A meteor shower takes place when Earth flies through a trail of particles that were shed by a comet or asteroid. Many of the particles burn up in the upper atmosphere, creating the streaks of light known as meteors.

But many more grains are too small to burn up. They float down through the atmosphere. Some of them stop at a height of about 10 miles. And that’s where the research aircraft head. Once there, they open up small boxes that catch whatever is drifting along – pollen grains, parts of bugs, bits of volcanic ash, and even exhaust from rocket engines.

Analysis reveals whether the captured particles are from Earth or from outside. The cosmic particles can then be tied to the meteor shower that was under way. And that can tell scientists about the shower’s parent body – a sample-return mission that never leaves Earth.

The Geminids are in good view tonight. The meteors are visible from mid-evening on. At its best, the shower might produce a hundred or so meteors per hour. And you don’t need to look in a particular direction to see them – just look up and wait for the fireworks.

Script by Damond Benningfield