Seven New Exoplanets Found

Upping the Ante on Earth-type Exoplanets


This illustration shows the possible surface of TRAPPIST-1f, one of the newly discovered exoplanets in the TRAPPIST-1 system. Scientists using the Spitzer Space Telescope and ground-based telescopes have discovered that there are seven Earth-size planets in the system.
Courtesy NASA/JPL-Caltech

The age of the exoplanets, worlds around other stars, just gets more exciting every day. Today, astronomers announced that they’ve found seven terrestrial planets around a small, very cool star called TRAPPIST-1. Three of those worlds are int he so-called “habitable zone” where conditions can allow liquid water to exist. Rumors of this news have been kicking around for several weeks, but today was the confirming announcement.

The kicker? Temperatures on the surfaces of the three in the habitable zone are just low enough that they could contain liquid water on their surfaces. That covers two of the main requirements for the habitability for life: exist in the so-called “Goldilocks Zone” and have the right temperatures to allow liquid water. Mind you, this doesn’t mean they HAVE life, but even finding such worlds is a major accomplishment.

The discovery definitely is record-setting — it’s the most habitable-zone worlds found around a single stars beyond the Sun. The arrangement of the TRAPPIST-1 planets is also quite fortuitous. It’s possible that the upcoming James Webb Space Telescope could take a look at them and study their properties more closely. That data could reveal the signature of ozone if this molecule is present in the atmosphere of one of these planets. If it’s there, it’s theoretically possible it would be a tracer for biological activity on the planet.

How Were They Found?

The astronomy team announcing the work used different telescopes in Chile, Morocco, Hawaii, La Palma and South Africa to do the ground-based observations. NASA’s infrared-sensitive Spitzer Space Telescope joined the hunt last September. Using infrared detection is important because exoplanets give off infrared signatures that can’t always be detected from Earth.

Three of the planets were already known because they could be detected as they orbited their star. These are called “transit” discoveries, and kept astronomers busy doing more observations to determine their orbital periods. All the observations revealed that TRAPPIST-1 is a very interesting analog to our own solar system, but with seven terrestrial-type planets orbiting in what we would call the inner solar system. Three appear to be in that fortuitous habitable zone.

Modeling Planets

At least a few of those newly discovered worlds have densities very similar to Earth’s (that is, they’re more rocky and not like the gas giants). That’s why they’re called terrestrials. Computer modeling helped the astronomers understand the specifics of the system and predict what would be found.

In a press release today about this largest ever batch of such exoplanets yet discovered, the University of Bern (one of the partners in the work) explained more about these worlds and how they can be observed: Earth-like exoplanets orbiting dwarf stars are easier to observe than real Earth twins around solar-type stars. Since these dwarfs are also much cooler, the temperature zone that allows water to be liquid on the surface of the planet is much closer to the star. And, exoplanets that are close to their host star revolve more rapidly and produce more transits in a given timeframe. NASA held a press conference today to announce this momentous discovery.

Why We Hunt for Planets

The search for worlds similar to our own can help scientists understand how planets like ours form, and what conditions are possible for life. Although it may seem like a bit of a biased view, since we know that life arose on our world and we know what conditions under which it formed, we can look to other worlds to see if they have the same conditions. That’s not to say life can’t arise under other conditions. But, science is all about understanding and extrapolating conditions to figure out how things happen. The next steps (whether they are now or in the very near future) are to see if the assumptions we’ve made about our planet play out across other star systems and their worlds. News like today’s are part of an exciting tale that is still being told!

Traversing Space on a Bridge of Stars

A Bridge of Stars between the Magellanic Clouds

The Magellanic Clouds.

The Magellanic Clouds in the night sky. The Large and the Small Magellanic Clouds are visible. The Clouds are moving towards the bottom left corner. Credit: V. Belokurov and A. Mellinger

If you’ve ever been south of the equator, you’ve probably seen the Magellanic Clouds in the southern hemisphere sky. These two little galaxies  look like puffy clouds separated by a whole lot of space. It turns out that the light-years between them might not be so empty as astronomers once thought. Researchers at University of Cambridge in England have found what looks like a 43,000 light-year-long bridge of stars stretching from one galaxy to the other.  Their work, based on a huge census of stars that the Gaia satellite is doing, is giving a new look at what happens when dwarf galaxies interact. The result of its mission, when completed, will be a 3D map of our galaxy, and apparently of our neighboring satellite galaxies.

Using Old Stars to Trace a Bridge

bridge of stars

The Magellanic Clouds, their stellar halos and the RR Lyrae bridge. Pale white veils and the narrow bridge pf stars between the Clouds represent the distribtuion of the RR Lyrae stars detected with the data from the Gaia satellite. Credit: V. Belokurov, D. Erkal and A. Mellinger

The team of astronomers focused their attention on data about stars called RR Lyraes. These are pulsating variables that are quite old stars. They’ve been around for a long time — at least as long as the Magellanic Clouds have existed. So, their very existence tells us something about the history of these two nearby dwarf satellite galaxies. Theastronomers used the RR Lyraes to measure the extent of the Large Magellanic Cloud first. It turns out there’s a sort of fuzzy halo of these stars stretching away from the LMC that’s being stretched out into a evanescent bridge of stars.

The big question now is why this stream exists. Normally streams of stars aren’t stretching away from a galaxy unless there’s been something to tear them away. In this case, it’s likely that the tidal pull of the e Small Magellanic Cloud has steadily lured away stars from the LMC.  As it orbits, the LMC is leaving a tracer of its stars as it goes.  There could also be stars in the stream that are being attracted by the gravity of the Milky Way, too.

A Bridge of Stars During Interactions

Interactions between galaxies often warp and reshape the participants in the galactic dances. Such interactions are also an integral part of the galaxy assembly process: big galaxies get built from the collisions of smaller ones. We’ve seen streams of stars in other interacting galaxies, so this lovely bridge between the Magellanic Clouds fits right into the idea that cosmic dances can do more than warp galaxies. They can strip stars away, too.

This is a pretty cool story of galaxy evolution taking place in our own galactic back yard. If you want more information on the work the Cambridge astronomers are doing, check out their press release here.