Exoplanet Explorer: Orbitar

Today’s post is the first in what I hope will become a semi-regular series about exoplanets: planets that orbit stars other than our Sun. I’ve decided to start with an exoplanet named Orbitar.


In December of 2015, the exoplanet designated 42 Draconis b was officially renamed Orbitar following a public naming contest held by the International Astronomy Union. Orbitar is a gas giant planet orbiting a red giant star approximately 315 light-years away in the constellation Draco.

Discovering Orbitar

The gravitational pull between planets and the stars they orbit causes stars to wobble in place. When the star 42 Draconis was found to wobble at a regular interval of 479 days, it was determined that a large planet with a 479 day orbital period was likely responsible.

Further calculations determined that this planet had an average orbital distance of 1.19 AU and an orbital eccentricity of 38%. The planet’s total mass was estimated to be equivalent to at least 3.88 Jupiters, give or take 0.85 Juptiers.

Life on Orbitar’s Moons?

According to the Brevard Astronomical Society, the group that won the IAU naming contest for Orbitar, “this closely orbiting gas planet could possibly host moons with Earth-like characteristics in the so-called habitable zone.”

Personally, I feel that’s a bit over-optimistic. At an orbital distance of 1.19 AU, Orbitar and its hypothetical moons would certainly would be within our Sun’s habitable zone, but 42 Draconis (which was renamed Fafnir in the IAU contest) is over twice our Sun’s age and has entered the red giant phase of its life cycle.

I may be wrong about this, but I’d expect that Fafnir’s habitable zone would lie well beyond the 1.19 AU distance. Orbitar’s moons (if they exist) should have been charred to cinders by now.

However, that still leaves us with the possibility that Orbitarian life could have existed at some point in the distant past, when Fafnir was still young and still a main sequence star like our Sun.

P.S.: As far as I can tell, the name Planety McPlanetface was not submitted to the IAU’s planet naming contest.

Correction: The “Life on Orbitar’s Moons” section of this post was based on a quote which was misattributed to the Brevard Astronomical Society.  See the comments below.  I can no longer find the original source for that quote.


Orbitar, Really? Some New Exoplanet Names Are Downright Weird from Ars Technica.

Planetary Companion Candidates Around K Giant Stars 42 Draconis and HD 139 357 from Astronomy & Astrophysics.

Name Exoworlds: An IAU Worldwide Contest to Name Exoplanets from the International Astronomy Union.

10 thoughts on “Exoplanet Explorer: Orbitar

  1. 1.19 AU sounds really close for a red giant, assuming it’s anything like the size our sun is projected to be by that stage. The sun would take up most of the sky on those moons. Red giants are cooler than main sequence stars, but I agree probably not cool enough.

    Keeping track of all these exoplanets is a major challenge for hard sci-fi writers. It used to be we only needed to keep track of stars and could make whatever assumptions we wanted for what was around each one. Now, if you want to set a story on a planet around Tau Ceti, you need to make sure it doesn’t contradict the most recent astronomy, and have to be prepared for new discoveries to make your story obsolete.

    Liked by 1 person

    1. I already had to change a setting for one of the TNN stories because of a new exoplanet discovery. From now on for my science fiction, I’m going to try to be vague about which stars and planets I use, even when they’re based on real locations.

      Liked by 1 person

      1. Ambiguity is a well tested strategy. One of the Expanse authors admitted that they never give specific dates for when anything happens in their stories, knowing that someone with too much time on their hand would calculate exactly where the planets and asteroids were on that date to show that the authors hadn’t.

        Liked by 1 person

      2. I hadn’t really thought about that, but yeah. Especially with something like the Expanse, which feels like pretty hard Sci-Fi, people are going to be even more nitpick about your scientific inaccuracies.

        Liked by 1 person

      3. The Expanse authors are careful never to claim that their stuff is hard sci-fi, although I think it’s fair to say it’s hardish. The more fantastical elements involve alien technology and hide behind Clarke’s third law.

        Liked by 1 person

      4. Dear J.S. I was wondering where you got this quote ? According to the Brevard Astronomical Society, the group that won the IAU naming contest for Orbitar, “this closely orbiting gas planet could possibly host moons with Earth-like characteristics in the so-called habitable zone.” As far as I know not one person in our club has ever claimed this. If I am wrong please correct me.

        Liked by 1 person

      5. Thank you for getting in touch, and I apologize for my mistake. I believe I pulled this quote from the link cited at the very end of this post, but that link is now dead, so I can’t verify that. I’m adding a correction to the post.

        Liked by 1 person

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