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10th Planet

July 29th, 2005, by slackerastro, MP3,

Move over Pluto! You’re no longer the farthest!

We interview the co-discoverer of the 10th planet in our solar system, Dr. Chad Trujillo.

Astronomers have found an object larger than Pluto out at the edge of the solar system.

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  1. Jorge Schrauwen Says:

    Wise move, the Chitchat #3 comments got a bit offtopic :)

  2. Will Says:

    These seem to be two different objects. One, 2003 UB313 is at 97AU, the other, 2003 EL61 is at 51 AU. Exciting that they were both announced within a day of each other though.

    Love the show, wish it was daily;)

  3. ozastro Says:

    Who will be the first to register the domain name
    or will have a major update of their web site?

  4. Clyde Says:

    Great work guys. A historic day, not only for the world but for SA. Getting Trujillo *ON THE ANNOUNCEMENT DAY* is a big deal.

    Congrats to the scientists and to the SA crew thanks.

  5. Jorge Schrauwen Says:

    Not sure about you guys but i got the news letter 3 times…

    One would have been fine too.

  6. slackerastro Says:

    You were subscribed multiple times. I removed the duplicates. - a

  7. Jorge Schrauwen Says:

    ah thanks, i remember getting and error the first time whil subscribing, maybe that was it.

  8. Shaded Spriter Says:

    Is there any news about what the planet is going to be named.

    As a common name not a Astronomer’s name.

    I am guessing since It has been named officially the 10th planet it will start to appear in high school text books.

  9. Shaded Spriter Says:

    I heard the episode - I guess we will have to wait.

  10. Jose Mauricio Rozada Says:

    Don’t forget that 2005 FY9 was also discovered, which seems to be the largest KBO besides 2002 UB313 and Pluto (H~0,3), and it is rarely mentioned in the news. Amazing, isn’t it?

  11. hendy Says:

    The interview has been linked to from the Blue.

  12. suitti Says:

    One is 2003 UB313 at 97AU, the other, 2003 EL61 is at 51 AU.

    So, if the IAU says they’re both planets, 2003 EL61 becomes Planet X.

    But the IAU has to vote on it. If they adopt one of the formal definitions
    of planets, anything could happen. One possiblity is that Pluto is Planet X.

    Saturday night, my astronomy club had a picnic at their observatory.
    The hot dogs were burnt and the weather was great. The 12.5 inch
    Cassigrain should have been able to reach 18th mag with the CCD camera.
    However, light pollution has grown (groan) to the south of the site of late.
    I don’t think the 22 inch DOB can reach 18th mag visually. 17th mag
    may be possible, but would be really pushing it.

  13. prussell Says:

    Awesome interview, and on discovery day. He sounded awefully calm. Are scientists not allowed to get giddy? 3 announcements in one day. Pretty cool of Trujillo’s team to cede the discovery of 2003 El61 to the other group.

    Does anyone else think they are being a little hasty in calling this the 10th planet of the solar system? It’s super far,and so inclined and they say it’s clearly an Kuiper belt object. I think it pushes the argument that Pluto is a Kuiper belt object and a planet further. I read the quote from Brown on the NASA site about how this is certainly a planet etc and it surprised. I thought they’d be a bit more reserved. Unless he wants to go down in history as discovering the 10th planet…which, I suppose, who wouldnt want to do that?

  14. suitti Says:

    It’s pretty hasty. For one thing, the International Astronomical Union hasn’t voted on it.

    What will the IAU say? Well, for one thing, there is no IAU approved definition for the term planet at the moment. IMO, this is bad. For one thing, it means you can’t predict how the politics will play out. So, all you can do is prepare several new versions of your basic astronomy textbook, and release the correct one when the IAU gets around to voting. If you want to preprint them, expect to send many of them to the recycling bin.

    For the ancients, a planet was a wandering star. This definition worked pretty well. You look up into the sky, and if it looked like a dot, and it moved around, then it was a planet. It didn’t matter how big your telescope was, because, well, there weren’t any telescopes. Today, that definition implies that planets are naked eye point objects that move. By this definition, Mercury, Venus, Mars, Jupiter and Saturn are planets. If the ancients had noticed Uranus, it would be one too. Of note is that Pluto, Neptune, and the Earth are not. The ancients also considered the Sun and the Moon as members of the seven heavenly objects. Again, Dirt… I mean Earth wasn’t one of them.

    With the advent of the telescope, and some hard work, the public got the idea that planets are spherical things that orbit the Sun. This is nice because then the Earth is one, even though it’s not much in the way of a point of light. The proposed definition that I like preserves this, but adds some constraints. One does not want every grain of sand that happens to orbit the Sun be called a planet. One convenient low end size constraint is the size a body must be before it collapses to at least more or less a sphere under it’s own gravity. That happens at around a diameter of 700 km (434 miles). At the large end, if an object were big enough, it would undergo fusion, and therefore would be a star. That happens (with Deuterium?) at about 13 times the mass of Jupiter. So, an object that orbits the Sun, but not also another body, that is at least 700 km, but less than 13 Jupiter masses is a planet. The shortened version is “a spherical non-fusor in orbit around a fusor”. Under this definition, the current nine planets remain planets. Ceres, Varuan, Quaoar, Sedna, and at least two of the new ones, 2003UB313 and 2003EL61, and probably a couple others are planets. Vesta isn’t, as it is only 525 km, for example, even though it’s pretty spherical.

    Other people say that Pluto shouldn’t be a planet, but rather a Kuiper Belt object. IMO, fooey. Jupiter, Saturn, Uranus and Neptune are gas giants, but they are planets too. Mercury, Venus, Earth and Mars are terrestial planets (rocky), but they are planets too. There isn’t any reaon that Pluto can’t be studied as a Kuiper Belt Object (KBO) along with other KBOs even if it keeps it’s membership in the planetary club. IMO, the concept and definition for planethood is a public sort of thing, and ought to have the simplicity that the public can cope with. IMO, it’s a good thing that the public has some sort of clue that planets are like the Earth, only “out there”, rather than that they are “points of light that move”.

    As for Planet X, planets don’t really have numbers. Pluto was closer to the Sun than Neptune from 1979 to 1999. During that time, it was the 8th planet. If my favorite definition is approved by the IAU, Ceres becomes the 5th planet from the Sun, and Pluto becomes Planet X, the 10th planet from the Sun. However, as it is currently 39 AU out, and 2003UB313 will be only 36 AU out in 280 years, so the numbering could continue to change.

    If you disagree, well, YOU’RE WRONG… I mean, sure, I’d like to hear your opinion.

  15. suitti Says:

    Bird watchers have “life lists”. These lists are basically every species you’ve ever seen. A few years back, the ABA (American Birding Association) changed the name of the Baltimore Oriol to the Northern Oriol. I happily went out, found one, and added it to my life list. They aren’t uncommon, and I’d gotten to the point where only uncommon birds, and those on other continents, were left for my list. The ABA renamed the Northern Oriol back to the Baltimore Oriol, and I went out to find one for my list!

    I’m going to start an astronomical life list. As soon as I can, I want to see 2003UB313, and 2003EL61. The IAU (International Astronomical Union) will give these suckers names soon, and I can go reobserve them. If I’m lucky, they’ll give them planetary status some time later, and I can put them on my list yet again. How often will you get a chance to see another planet?

    There are lots of galaxies with more than one name. I mean, there’s a new name for each object for every bloody catalogue. Stars too. So, all I need to do is keep going out. Last night’s observing program is good enough.

    It’s too late to reobserve SL9, however.

  16. Jorge Schrauwen Says:

    can’t we add that it must have and atmosphere to the list of requirements?

  17. ahspaceblog Says:

    Hey, I wonder if this is the Planet X that’s supposed to come crashing into Earth in the future????

    (trying to elicit a response from Phil if he’s out there.. :> )

  18. Carpe Noctem Says:

    New planet

    I listen to slackers astronomy and their latest podcast is about a 10th planet that was discovered last week by Dr. Chad Trujillo and his colleagues. The new planet (temporarily called 2003 UB313) is the farthest from our sun.
    This planet orbit at a …

  19. Jorge Schrauwen Says:

    ahspaceblog: sure it will, if we attache huge trusters to it and wait a long long long tim

  20. suitti Says:

    It might be more efficient to attach huge thrusters to a smaller airless body, and use it’s gravity to move Planet X our way. It’d likely be cheaper to loop such a body between Planet X and Neptune, and exchange momentum. It has been suggested that this is a viable way to change the Earth’s orbit. We may want to do this, for example, to avoid being roasted by the expansion of the Sun.

  21. slackerastro Says:

    Suitti, You have just sparked a very evil conservation of energy and momentum problem for me to give my students! Something to think about- The planet you are accelerating goes faster because of the force, and as its mass decreases from propellent getting burned it gets faster to conserve angular momentum. The question is, how much trust and mass loss must be supplied to to boost us out to half the asteroid belt (should be decide we want to destroy the Earth). I supect the amount of trust/mass loss needed would be equivalent to a large fraction of the Moon.


  22. Jorge Schrauwen Says:

    Pamela: I think its time for a Monologe or Podcast on momentem and energy conservation…. didn’t get any of that last bit

  23. suitti Says:

    I didn’t make it up. There was an article some years ago. It claimed that we have time to move the Earth. Momentum is conserved. Anyway, maybe Google knows.

  24. Shaded Spriter Says:

    I heard on skepticality that the planet has been named Xena…(WARRIOR PLANET!)

  25. Joe Anderson Says:

    Come on… Pluto is not a planet! It’s a planetoid (if Sedna isn’t a planet neither is Pluto).

  26. Jorge Schrauwen Says:

    And this is why this isn’t resloved till this time…

    Astronomers just can’t agree with eachother.

  27. Dennis Ward Says:

    When I was in grad school, the “What is a planet?” debate was hot and heavy. After thinking about it for a few weeks, I proposed the following definition of a “planet”:

    1) Orbit a star rather than another planet
    2) Be massive enough to be roughly spherical due to gravity
    3) Have an atmosphere, frozen or gaseous (goodbye Ceres, hello Pluto!)

    I may be hoist on my own petard with these new discoveries, depending on if we can ever determine their surface compositons…

    IMO, Pluto is a planet– it’s been classified as one since the night of it’s discovery, and history is relevant. Some folks over-react to this issue (think Rose Center), but everyone is entitled to their own opinion.

    Clear Skies!

  28. alex Says:

    i think the new planet is cool so the kids in the future will learn about it!

  29. emma Says:

    i think we should learn about it more and that the peson pppl who fownd it r great

  30. emma Says:


  31. suitti Says:

    Mercury doesn’t have an atmosphere, does it?

    In some sense, Cerese has an atmosphere. It just happens to be 10^-6 ATMs of pressure.

    Even Mars has an atmosphere that does a good simulation of a vacuum. I mean, even if it had oxygen, I wouldn’t be taking off my helmet. At some point, you have to draw the line on what is or isn’t an atmosphere. I’m inclined to drop this requirement.

    If 2003 UB313 has an atmosphere, and it doesn’t thaw at 36 AU (as close as it gets), how would we know it has (or does not have) a frozen one? Even if it does, do we wait 280 years before proclaiming that it is a planet?

    If it turns out that Vesta is basically spherical, even though it isn’t quite big enough for the definition that I’ve heard, I’d be inclined to make it a planet. MVEMCVJSUNPQVSX or something is the new acronym for school kids, or something kinda like it. They can cope.

    What I also really want is a definition for a moon. The rocks and dust that they’re finding around Jupiter, IMO, fail to qualify. But where to draw the line between a small moon and a big rock is going to have to be arbitrary. I DO NOT want some astronaut’s glove to be considered a moon.

  32. ruby Says:

    It is great

    I think it should be named xene

  33. Jorge Schrauwen Says:

    what about;

    If the object was in a good orbit it should be able to hold on to a stable atmosphere?

    lets say if you place mercury where the earth it and give it gasses… will it hold on to them?

  34. European Says:

    I think neither Kuiper Belt object (KBO) is really a planet, at least untill you find one greater than Mercury. We can leave Pluto its double status (for sentimental reasons), but the best definition of a planet I’ve heard is:
    “A body (less than a star) orbiting Sun (or another star), with a weight greater then the sum of weights of other objects on similar trajectory (other minor planets, moons, etc).”
    This definition disqualifyies Ceres, Pluto, Sedna, Orcus, Quaoar, 2003 UB313, 2003 EL61, 2005 FY9 etc., though the term “similar trajectory” should be precised and objects on Sedna-like trajectory to be found (but almost surely they exist). The purpose of this definition is to distinguish between “belts of many comparable objects” = minor planets of whatever size, comets, and “great solitairs with possible small compagnions” = planets.
    Finally a bit history: The astronomer who found Ceres (over 900 km), waited with its status, because it seemed a bit small to him and 2-3 years later, as other two cca 500 km bodies were found, he was satisfied to call it an asteroid, not a planet. Only the long 72 years between discovery of Pluto and of the next KBO made a psychological difference. If e. g. UB313, Sedna, EL61 and Pluto were found at once, nobody would dare to come with the idea call them all planets (OK, M. Brown possibly would, but no chance at IAU).
    In addition, from 30-ies (discovery of Pluto) to 60-ies people thought Pluto is cca Mercury sized because of its apparent magnitude. Only later they found out, that it has a much greater albedo (0,6) and it is significantly smaller (mere 2390 km), than previously assumed.

  35. suitti Says:

    There’s a really funny article that graphs the various estimates of Pluto’s size against the date of the estimate. It’s apparent that the size decreases. The article projects forward in time to something like 2015, when the size should become zero, and speculates that after that, it should become imaginary. I don’t recall the math used.

  36. ozastro Says:

    Michael Brown of the California Institute of Technology has discovered Zena’s sidekick, oops, moon Gabriella

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