7 Earth-Sized Planets Found Orbiting a Tiny Star

By John Wenz | February 22, 2017 12:01 pm

(Credit: NASA/JPL-Caltech)

TRAPPIST-1 has a solar system like no other. The tiny, tiny red dwarf is just barely big enough to be considered a star, and is, radius-wise, a hair bigger than Jupiter. When it was announced last May, there was some excitement: the system had three Earth-sized planets, and they might all be habitable.

We’re going to have to revise that, though. It has seven planets. The results of an intensive study were published today in Nature.

TRAPPIST-1 is so small that it resembles Jupiter and its planets appear more like the jovian moons when laid out, distance-wise. TRAPPIST-1b has an orbital period of just 1.5 days and orbits at 1 percent the distance between the Sun and the Earth. Because TRAPPIST-1 is so small, though, instead of dooming the planet, it could give it just a slightly balmier-than-comfortable temperature.


The May 2016 events that led to the initial discovery of the planets actually ended up being somewhat in error. Planets TRAPPIST-1b and TRAPPIST-1c were easily confirmed, but TRAPPIST-1d was not. TRAPPIST-1d had a bizarre, hard-to-constrain orbit much longer than the other planets. 

“The first transit and the second transit were coming from different planets,” Michaël Gillon, a professor at the University of Leige and lead author of the paper, says. “In fact, the second transit was two planets passing at the same time.”


What the planets in the TRAPPIST-1 system might look like. (Credit: NASA/JPL-CALTECH)

Like No Other

Intensive studies using both the TRAPPIST telescope and NASA’s Spitzer telescope helped refine the orbit of the planets and drew out the presence of two more from the data. TRAPPIST-1b, -1c, -1f, and -1g are all very slightly larger than Earth; -1e is slightly smaller than Earth; -1d and -1h are closer to Mars in size.

While the exact masses and orbital periods aren’t known yet, preliminary results suggest that they may be in resonance. That means that when -1b orbits eight times, -1c completes five orbits, often marked as 8:5. -1c and -1d are in 5:3 resonance; -1d and -1e are in  3:2, as are -1e and -1f. -1f and -1g are in 4:3.


All of them seem to be in the habitable zone of TRAPPIST-1. That means that they could, under the right conditions, sustain surface water, but there’s no proof that any of the planets do. For instance, in our solar system, Venus and Mars are in the habitable zone, but both are fairly inhospitable. 

Of the seven, the researchers believe that -1e, -1f, and -1g are the likeliest to be habitable based on where they sit in the solar system. While seven planets have been confirmed, that’s not all the system may hold in store.

“It is just the beginning for many reasons — there might be more on top of that,” Julien de Wit, a co-author on the paper, says.

Slow Your Roll

There are other considerations before we declare the planets quite ripe for life, though. M-dwarf stars like TRAPPIST-1 tend to start out very active, with high energy flare events. This could strip away the atmosphere of young planets.

At this point, according to co-author Emmanuël Jehin, most comets would have been cleared out of the system and thus unable to replenish the atmospheres. But other forces like volcanism could work to stabilize the atmospheres, strengthening them against the relentless flare events.

M-dwarfs, after the first 3 billion years or so, finally settle down, though many stellar events still occur. For instance, Proxima Centauri is an active flare star, which could doom its habitable zone planet, Proxima Centauri b, from ever forming complex life. But TRAPPIST-1 is cooler and less active than Proxima.

“If you compare it Proxima Centauri, it’s much less, but if you compare it to the Sun, it’s much more,” Gillon says.

TRAPPIST-1 and its seven planets are high on the list of planets to be observed by the James Webb Space Telescope (JWST) after it launches next year. A follow-up telescope to TRAPPIST, SPECULOOS, will be able to find more TRAPPIST-type objects. TRAPPIST itself only looked at 50 ultracool stars for planets, while SPECULOOS will look at tens of thousands.

JWST will monitor transits of worlds in the TRAPPIST stars, hoping to capture a glimmer of their atmospheres. If they seem to be thin and water-dominated, we may indeed be looking at a quite Earth-like planet. Or even three of them. Maybe, just maybe, seven.

“We have seven targets that we can study in great depth, and they can give us a completely new insight into planet formation and stellar history,” de Wit says.


This article originally appeared in Astronomy.com

CATEGORIZED UNDER: Space & Physics, top posts
  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    TRAPPIST-1 is 39 light-years distant. Turn some really big radio telescopes its way and have a good listen, radio through microwave. Right ascension 23h 06m 29.383s, Declination −05° 02′ 28.59″, putting it at the base of Aquarius’ neck (by my reckoning) – but of course.

  • John C

    planets everywhere, oddly not a single signature of readily identifiable intelligent life anywhere in the universe no matter where or how far back in time we look

    • Bobareeno

      Intelligent life is rapidly slipping away on this planet, yet alone on those so far away;let’s get our own act together.

    • Rich Werning

      In the 4.5 Billion year history of the Earth, man has only been around for a few million of that. And of man’s time on earth, the past 60 years or so we have given off any sign of life that an alien civilization might be able to pick up. We’re talking a real narrow window of time where 2 (or more) intelligent civilizations need to reach this point. Who knows, maybe Earth is the first one?

      • John C

        That could be the problem. There might only be a slim window of only 200, 300 years or so that a civilization gives off electromagnetic radiation, after which it’s power sources, communications, etc. would be undetectable or unrecognizable by more “primitive” civilizations.

        • OWilson

          While we are surmising, it is safe to surmise that they will be aware of their own history of electronic communications.

          It’s a safe bet that they would work on the basis of backward compatibility.

          (That is, if they were stupid enough to invite the whole universe into their lives)

          • Carlin

            If I were them, I wouldn’t bother with this murderous, self destructive, violent culture! What Vulcan would invite THAT into their ‘space’???

          • John C

            There are a lot of possibilities. The most disturbing being we’re surrounded by intelligent life that is no more recognizable or comprehensible to us than we are to amoebas or plants. And if so they apparently have no interest in communicating with us, up to now anyway.

    • TLongmire

      Pretty sure your idols made contact.

    • TLongmire

      Pretty sure your idols made contact.

    • applecreeker

      Even on Earth I question whether we show signs of intelligent life.

  • Mike Richardson

    Truly awesome news. Red dwarves are the most common type of star in the galaxy, and apparently quite prolific at creating at least earth-sized planets. If atmospheric or oceanic convection can moderate the global climates of these tidally locked worlds, they may even be habitable, at least along the temperate band straddling the terminator between day and night sides. Super flares common to these types of stars could be problematic, but could also spur evolution if life were able to adapt to the intermittent bursts of higher radiation. Imagine what if would be like to live on such a world, living in the temperate band where the sun permanently hovers just a few degrees above or below the horizon, with other obvious worlds clearly visible in the sky and relatively much closer than earth’s own sibling planets. Any technological species in a system such as TRAPPIST-1 would have clear goals for space exploration, an incentive to spread from one world to the next and establish a multi-planet civilization. It really excites the imagination and makes you wonder just what is out there.

    • Dennis Spirgen

      Even if flare events were extremely rare, I’m guessing that a bath of sterilizing radiation every 100 million years would be enough to prevent “any technological species” from having to worry about space exploration.

      • Mike Richardson

        That depends on the severity of the flares, the thickness of the planet’s atmosphere, and the strength of the planet’s magnetic field. Worlds in such compact systems may experience strong tidal heating as they pass each other in their resonant orbits, and are pulled in opposite directions by their relatively close parent star. That could churn molten cores to generate strong magnetic fields, as well as stoke active volcanism which would also thicken the atmosphere — think of Io, but with enough gravity to retain an atmosphere (hopefully less toxic than Io’s). Additionally, lifeforms can be surprisingly resilient to even high levels of radiation, given time to evolve. So, absent completely sterilizing blasts from the red dwarf star, these apparently common types of worlds may also be the best places to look for life, perhaps even advanced forms of life.

        • Dennis Spirgen

          That is the problem with the “life is resilient” argument. Life must be given time to evolve. Flare activity is far too intense for life to evolve around a red dwarf. As for hypothetical volcanism extreme enough to create a protective atmosphere, that by itself is an extinction-level event. I won’t even go into the problems of tidal locking. Your belief that such worlds are places not just to find life, but to find intelligent life, reveals SETI to be more of a religion than a scientific inquiry. But of course you can never be proven wrong, because maybe the next planet . . . (Of course, I would love for you to be right, but I’ll wait for proof.)

          • Mike Richardson

            I don’t believe one way or another, Dennis, but I am keeping an open mind, considering how much we still don’t know about these worlds. I will agree that there are more hurdles for complex life to develop, but sometimes challenged to life result in surprising solutions, at least in earth. Proof is needed to resolve this question, but the sheer abundance of red dwarf stars, and presumably planets around them, mean that any serious attempt to search for extraterrestrial life must include them. Until then, it is fun to speculate, whether or not those speculations are eventually born out.

          • Dennis Spirgen

            Well, we don’t disagree there. I only take issue with those who say we inevitably will find other life. There probably is other life, since anything that is not impossible must happen if the universe is infinite. But we may never find it, and without proof it remains speculation, however fun that may be.

  • Prof Quill

    Fascinating stuff but I can’t help but comment on “TRAPPIST-1 has a solar system like no other”. Needs the qualifier, “yet discovered”. With perhaps billions of star systems in the great unwashed universe, the vast majority likely forever undetectable, one can hardly conclude that this system is in some way unique.

    Yeah, it’s just semantics but good science should use more gooder observations ;-).

  • BJK

    As an Earth/Space Science educator, I have to point out that other stars do not have SOLAR systems. Sol is the name of our star – therefore, we have a SOLAR planetary system. Other stars have their own planetary system. Yes, as a PP said, it’s semantics. But good science should use correct terminology. And, since I’m on the subject, we should be referring to Sol by that name, rather than “the sun”. And Luna, our moon, should be referenced that way, as well….. OK, I’m off my grumble platform. This is interesting astronomy news, and I look forward to many more similar discoveries as we continue to look out into our universe.

    • John C

      Is that going to be on the test?

      • BJK

        Absolutely! And you’ll have to write an essay to explain whether you agree or disagree, and support your position with evidence.

    • Dennis Spirgen

      I always called my father “Dad.” Although there were other dads, to me he was THE dad. Similarly, Sol is THE sun and Luna is THE moon. You need to draw a distinction between scientific accuracy and common parlance.

  • stevlich

    Guaranteed that NASA never finds a molecule of life anywhere. The fix is in.

    • Jim

      conspiracy much? This is a science column.

    • Dickybow

      Certainty in anything is generally not a smart move…


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