Asteroid update: size doesn’t matter

By Phil Plait | March 25, 2008 11:01 am

Just a quickie update on the asteroid naming thingy:

Michael Stackpole and Rebecca (well, A Real Girl for Rebecca) have posts on their asteroids. They mention their asteroid designation numbers — all asteroids get a number and a name, hence 165347 Philplait — which means I can look up their characteristics too!

I wish I hadn’t. Of the four (including PZ’s), mine is smallest.


Rebecca’s is about 4.3 kilometers in diameter, and Michael’s is about 1.7 km across. Mine is 1.3, PZ’s is 2.6.


Anyway, I described how the diameter is estimated in my last post, but specifically there is a parameter called the absolute magnitude, which describes how bright the asteroid would be if it were 150 million kilometers from both the Earth and the Sun and the side of the rock facing us was completely lit by the Sun. This geometry is actually impossible (the Earth needs to be between the asteroid and the Sun for this to happen, so the asteroid can’t be the same distance to both at the same time!), but it’s just a definition. Once you know the absmag and assume an albedo, you can calculate the asteroid diameter. I used astronomer Dan Bruton’s calculator webpage for this, once I got the absmag from the bottom of the JPL Small-Body orbit diagram page (the links for those are above and in my last post).

I checked my numbers twice and I’m still smallest. Reality can be cruel.

Still, I did happen to see that of all four, mine gets closest to the Sun in its orbit, and hence closest to Earth. That makes it the easiest to get to, so I’ll probably get mine colonized first. It’s smaller, with lower gravity, making it easier to land on (really dock to) as well. That’s something.

I also see that Rebecca’s has the widest orbit; I can think of any of a half-dozen jokes I could make, any one of which would get me emasculated the next time I see her so I’ll refrain — and you should too, I’d wager.

Seriously though, I’m totally chuffed by this. Congrats to my trio of extraterrestrial compatriots as well. And Jeff Medkeff, the co-discoverer of the quartet, has posts up about them: mine, Rebecca’s, PZ’s, and Michael’s, as well as a general post about with an overview of the situation. Thanks Jeff!


Comments (30)

  1. Last night, at Skeptics in the Pub, Rebecca was dropping all sorts of hints about “astronomical news” which would be breaking today. Even though the news was said to involve PZ Myers, I didn’t twig to what it might have been — maybe our new cephalopod overlords from deep space were going to announce their presence?

    Anyway, it’s all very cool. Congratulations are in order all around.

  2. Actually, the official name is “(165347) Philplait” – with asteroids, the numbers goes into parenthesis, with comets the name.

  3. Rowsdower

    Asteroid envy? What would Freud say?

  4. allkom

    I feel vexed . Just posted pharyngula to refrain from “bathroom betting ”
    since he’s already under spots . Don’t feel diminished in any sense . Your glory is just the same !!!

  5. Michael Lonergan

    Phil, when one is comparing size, or bemoaning the lack thereof, the use of the word, “Quickie” should probably be avoided… I mean you’ve already got one strike against you.

    You could redeem yourself by posting the calendar picture of you with your “massive” telescope…

  6. Christine Pulliam

    Maybe you could convince some other asteroid discoverer to name a larger one “Badastronomer.” Or do the rules prevent two named for the same person, even if the names used are different? In that case, how about the asteroid “Badastronomy.” Or “Deathfromskies” (NEOs only for the last…)

  7. It’s a conspiracy, I tell ya!!! Phil’s rock should be bigger than PZ’s!!

  8. Dave Hall

    Congrats on the namesake in space.

    Remember, its not the size that counts, its also how it orbits!

  9. allkom

    Hey , they’re making a fuss out of this , suppose they fear ba will rob the spotlights

    copied from pz’s blog:
    “Of course Phil is dimmer, he’s a mere astronomer as opposed to a biologist….

    Posted by: Ron | March 25, 2008 1:28 PM ”

    Let’s keep up to it !!

  10. Which albedo are they using for size estimates? The Bond albedo or the geometric albedo? And are they using the whole EM spectrum or just visible light or IR?

  11. Surprised no one’s mentioned Dan Durda’s asteroid yet…

  12. Cory Meyer

    Here’s some condolence. Randi’s asteroid is 11km. No one stands a chance against an amazing magician!

  13. I was talking with Jeff last night, and he mentioned Rebecca’s namesake was found while looking for “almost lost” asteroids (ones which, if they didn’t get observed soon, we wouldn’t be able to calculate an accurate enough orbit to find them again.)

    “Almost lost” sounds a little like they’re ne’er do wells, and that sounds just like the kind of thing Rebecca (or in this case Rebeccawatson) would love to hang out with. The bad boy asteroids.

    Don’t know if that’s true for you BA, but in that company, size definitely doesn’t matter.

  14. If yours gets closest to the sun, surely that means that (165347) Philplait is hotter than the others!

  15. Making some assumptions about Philplait’s mass, what would the gravity be like for a person on the surface there? Also, any guess on it’s day-side temperature given it’s distance from the Sun and it’s assumed albedo?

  16. baley

    Too bad it’s smaller!

    How about selling Asteroids? There is already the Moon embassy selling it pieces of land. It seems more like Joke than anything else since the Moon property terrain documents are utterly worthless but they make money out of it!

  17. yetiman

    Remember, Phil, it’s not the size of your asteroid that counts –
    it’s how you use it.

  18. IRONMANAustralia

    Stark Enterprises is now in negotiations with Virgin Galactic to claim this asteroid and future mining rights, so look out for this headline:

    “IRON MAN owns Philplaiit”.

  19. Scott

    Some asteroid aficionados prefer to boast about their asteroid based on the number rather than the size, with lower numbers being better. In other words, whose asteroid was discovered first (approximately, an asteroid discovered earlier may get numbered later, see 69230 Hermes for a good example). Maybe there is some consolation there (you didn’t give the number for PZ Meyer’s asteroid so I couldn’t tell).

    And to answer a previous comment from Barton Paul Leveson, it is the geometric albedo in the Johnson’s V band that is used in the definition of absolute magnitude for asteroids.


  20. Don’t worry Phil, yours may be the smallest, but I wouldn’t be surprised if it’s the densest. Hahah, hehe, haheh, ahem, hehan, *cough* hehehehe, ehe, heh, uh, ahem, hmmm, yeah. “You’ve heard that before,” I know, I know.

  21. Carolyn

    From the post on his blog, Jeff Medkeff named Philplait after the first asteroid he discovered. The other three appeared later…

  22. Torbjörn Larsson, OM

    it’s not the size of your asteroid that counts – it’s how you use it.

    Spin it as much as you will, it will still be smaller.

  23. I WIN! Don’t worry Phil, when you colonize your asteroid and find there’s no where to put your giant telescope, I can rent you some space on Rebeccawatson.

  24. No worries, Phil. I still wouldn’t want that thing hitting Pittsburgh.

  25. Carolyn, I’m sorry if what is posted on my blog was misleading, but I made my first asteroid discovery in 1998 or 1999 – (165347) Philplait was far from my first discovery, and for the Healy-Medkeff team it was more like the hundredth, or two hundredth, or something like that. It is true that Stackpole, Rebeccawatson, and Paulmyers were discovered some months after Philplait, though.

    To tell the truth, there are two reasons I named (165347) after Phil:

    1) It is an asteroid that I discovered, free and clear – I did the observing *and* the measuring, so I’m the sole person listed in the IAU’s discovery records for this asteroid. I wanted my association with the discovery of whatever asteroid I named after Phil to be explicit and recorded forever. If you check the discovery records for Paulmyers, Rebeccawatson, and Stackpole, you will find they were discoveries of my collaborator, Dave Healy, or else co-discoveries with him. So basically, this reason has to do with the way the IAU keeps records.

    2) Of the many asteroids I’ve discovered, this is the only one that has not already been named that I actually remember discovering. Dave and I have made so many discoveries at this point that we just don’t remember finding most of them – the circumstances are too similar. All discoveries are made in basically the same way – sitting at a particular computer in a particular office inspecting images that all look much the same. Most of the discoveries just blur together. But the discovery circumstances for (165347) Philplait were unusual. I actually made the discovery at the telescope, nearly in real time, in images I took for the purpose of testing the system. That made the discovery memorable, and I wanted to link my memory of making that discovery with the later knowledge I’d named that asteroid after Phil.

    And that’s the story.

    As for having two asteroids named after the same person, my understanding is that it is against the rules. However, Hal Povenmire has two different asteroids named after him, so some have slipped below the radar, apparently.

  26. MandyDax

    Jeff, that’s really great. That’s a fantastic honor you’ve bestowed upon the great BA. :) Fantastic job finding it, too.

  27. davidlpf

    Congrats on the asteroid being named after you Phil, I wonder how big an asteroid being named after someonw the name david leonard philip fairweather would get.

  28. SpikeNut

    I was once described by a friend (!) as a “triaxial ellipsoid” because my first name is the same as an asteroid with those characteristics.


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