New SPECULOOS Telescope Sees First Light. Soon it’ll be Seeing Habitable Planets Around Ultra-Cool Stars

Our newest planet-hunting telescope is up and running at the ESO’s Paranal Observatory in the Atacama Desert in Chile. SPECULOOS, which stands for Planets EClipsing ULtra-cOOl Stars, is actually four 1-meter telescopes working together. The first images from the ‘scopes are in, and though it hasn’t found any other Earths yet, the images are still impressive.

The four telescopes that make up SPECULOOS are each named after a Galilean moon: Io, Europa, Ganymede, and Callisto. It’s operated by the European Southern Observatory, and is neighbours with the ESO’s flagship telescope, the VLT (Very Large Telescope). It enjoys excellent seeing conditions, high in the dry Andes, where there is hardly any rainfall or cloud.

SPECULOOS’s mission is to find Earth-like habitable planets around ultra-cool stars, including brown dwarfs. Brown dwarfs are also known as “sub-stellar” objects, or “failed stars” because they didn’t gain enough mass during their formation to turn on hydrogen fusion. Instead, they may fuse deuterium or possibly lithium. They occupy a niche between the largest gas giant planets and the smallest stars.

“This is a unique opportunity to uncover the details of these nearby worlds.” – Michaël Gillon, University of Liège, and principal investigator of the SPECULOOS project.

Ultra-cool stars is a category that includes brown dwarfs, but also includes very low-mass red dwarf stars. Astronomers think that ultra-cool stars and brown dwarf stars make up about 15 % of the stars in our neighborhood.

TRAPPIST-1 is probably the most well-known ultra-cool, or red dwarf, star. It is host to several rocky, roughly Earth-sized planets. Astronomers think it’s no accident that ultra-cool stars and red dwarfs are host to so many smaller, rocky planets, and they hope that SPECULOOS will find them. Credit: NASA/JPL-Caltech

SPECULOOS is searching these stars for Earth-like planets for good reason. Since they are all low-mass stars, and their protoplanetary disks are low-mass too, astronomers think the conditions might be ripe for an abundance of smaller, terrestrial Earth-like planets, because there’s more material left over after the star forms. Gas giant planets seem to dominate many other solar systems, but that doesn’t seem to be the case for ultra-cool and dwarf stars.

The telescopes of the SPECULOOS Southern Observatory gaze out into the stunning night sky over the Atacama Desert, Chile. Image Credit: ESO/ P. Horálek

The SPECULOOS observatory has a tough task. The small, cool stars that it’s looking for aren’t easy to see, even though they’re abundant. Astronomers have only found a few exoplanets in orbit around these stars, and only a small number of those have been in the potentially habitable zone. The four-scope observatory has a plan though. It’s going to focus on 1,000 of these stars, including the nearest, brightest, and smallest.

SPECULOOS will begin science operations in January, 2019. It’ll use the transit method of detecting planets, where the planet blocks some of the star’s light as it passes between us and its host star. Since the planet-hunter is only observing small, cool stars, then more of their light will be blocked by orbiting exoplanets, making them easier to detect compared to bright stars like our Sun, or brighter.

“SPECULOOS gives us an unprecedented ability to detect terrestrial planets eclipsing some of our smallest and coolest neighbouring stars,” elaborated Michaël Gillon of the University of Liège, principal investigator of the SPECULOOS project. “This is a unique opportunity to uncover the details of these nearby worlds.”

As part of its testing and calibration, SPECULOOS captured this image of the heart of the Carina Nebula. Image Credit: SPECULOOS Team/E. Jehin/ESO

One of the obstacles in our search for exoplanets is the inherent sampling bias of the equipment we use. Kepler was a phenomenal success, but it detected many more huge, uninhabitable gas giants well outside their star’s habitable zone than it did smaller, rocky worlds, closer to the star. This doesn’t mean that there aren’t lots of smaller, rocky worlds out there, it just means it was easier for Kepler to detect the larger ones. That might change with SPECULOOS. According to an ESO press release, “… the small size of the SPECULOOS target stars combined with the high sensitivity of its telescopes allows detection of Earth-sized transiting planets located in the habitable zone. These planets will be ideally suited for follow-up observations with large ground- or space-based facilities.”

The new quad-scope is also designed to see more of the light that comes from its target stars. “The telescopes are kitted out with cameras that are highly sensitive in the near-infrared,” explained Laetitia Delrez of the Cavendish Laboratory, Cambridge, a co-investigator in the SPECULOOS team. “This radiation is a little beyond what human eyes can detect, and is the primary emission from the dim stars SPECULOOS will be targeting.”

It’s always an exciting time when a new telescope comes online and sees first light. It’s like welcoming a new child into your extended family. You never know what the new one will discover, but you can’t wait to find out!


Evan Gough

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