Least massive protoplanetary disk found

By Phil Plait | February 9, 2008 8:07 am

File this under "Hey, that’s kinda cool": astronomers have found the least massive disk ever around a star. This press release is nifty, but has a major d’oh! moment for me. Read on.

Stars form in different ways, but the final birth pangs are roughly the same for everyone. A flattened disk of material forms from a collapsing cloud of gas and dust. The center heats up as more material piles on, eventually reaching high enough temperatures and densities to ignite nuclear fusion. A star is born.

The disk of material around the star can form planets. The types of planets that form vary depending on the type of star, whether it’s a binary star, how fast the big planets form, what the material is in the disk, and about a hundred other things. A few years ago this was conjecture, but now it’s a solid fact: we see these disks around many young stars.

A team of Japanese astronomers pointed the massive 8.2 meter Subaru telescope at the star FN Tau, which is known to be young. It’s also a dinky star, classified as an M5, making it a red dwarf (about 0.2 times the Sun’s mass). The astronomers looked in the infrared, where a warm disk is bright, and directly detected the disk. They had to block the light from the star (which is overwhelmingly bright), too.

What they saw is the picture posted above (click to embiggen). The black splotches are due to the telescope and the coronagraph, the device used to block the starlight. The disk is obvious enough. It’s big in human terms, with a diameter 260 times the Earth-Sun distance (Neptune is about 30 times that distance, so this disk is more than 8 times bigger than the solar system). However, as disks go, that’s rather small. In fact, the estimated mass (6% of the star’s mass, or about 1% of the Sun’s mass) makes it the smallest protoplanetary disk ever directly detected.

That’s cool.

However, I do have an issue with the press release. First, there’s a claim that I think is not true: it says this is the lowest mass disk around the lowest mass star ever seen. However, in 2005 a disk was detected around a brown dwarf star, which has far lower mass than FN Tau. It might be the lowest mass star for which a disk is directly detected, but that distinction is not clear. No biggie, but worth pointing out.

There is a bigger problem, though. The press release says that Earth-sized planets can form in this disk, which is OK (the disk is too low-mass to form anything as big as Jupiter). However, the press release title is a very misleading "A Lightweight Disk Around a Lightweight Star May Harbor Earth-like Planet". It says (emphasis mine):

One of the questions to come out during the study was what kind of planets can be formed from the disk around FN Tau? To date, astronomers worldwide have found 270 extrasolar planets using the indirect detection method, and all are primarily Jupiter-like giant planets; the least massive exoplanet is still 5 times heavier than Earth. Because it surrounds a smaller star, the disk about FN Tau was believed to more likely contain Earth-like planets. The best-fit model used during this study shows that the lightweight disk around FN Tau could only produce Earth-like planets. The planetary system formation theory also predicted that the disk is able to form planets lighter than the Earth within 30 AU, the distance where we find planets in our Solar System. The lack of heavier objects, such as a Jupiter-size planet, in the FN Tau disk system is consistent with the astronomers’ theoretical expectation.

The problem is, there is no indication that planets are forming in this disk. None. The release itself says the disk is missing the usual tell-tale sign of planetary formation, like lumps, gaps, and spiral patterns. Worse, the disk is young, only about 100,000 years old, and that’s pretty early to be forming planets. Now let me be clear: it may very well be forming Earth-like planets (or will form them in the future), but it is very misleading to state it the way they did. It’s sensationalized.

This is a very interesting result all by its lonesome. Why try to overblow it? I see that a lot, and I wish it would stop. NASA got mocked — and still does — because it overused headlines about Hubble finding "the best evidence yet" of black holes every time Hubble observed a black hole (I made this joke recently to some science journalists and they all laughed knowingly). If this kind of hyperbole continues, the public may get burned out on such things.

It’s OK to have fun with titles, but they shouldn’t be misleading.


Comments (25)

  1. Sespetoxri

    But… but… Phil, if they don’t, err, lie a little, they can’t very well get any attention, can they?

    I mean, seriously, take a look the next time you’re checking out at the supermarket. You think those rags like National Enquirer and the like sell like they due because of the content of the articles? It’s headlines, baby. The headline sells the fish-wrapper, and the stories are just complete garbage- not even making a lick of sense generally. My father, I’m ashamed to admit, used to buy and read those things every week. He CLAIMED it was for the crossword puzzles, but there were books full of them for the same price next to the mags.

    I’ve read those articles, and even the most rabidly gullible twit on the planet would have to raise an eyebrow every now and again upon reading them. The only thing which sells the mag is the headlines. Sadly the media uses this tired old method again and again, to greater or lesser extents depending on the source.

    The shame of it is it cheapens the science. This is a very interesting discovery overshadowed by an inaccurate title. The real kicker is, many scientists aren’t writers and someone else likely writes these little blurbs for them. The press release might be entirely out of their control, and here is this statement denigrating their very hard and very valuable work.

  2. Nigel Depledge

    BA, I agree. It can be misleading to over-hype these things.

    And it’s quite a nice result by itself.

  3. Sespetoxri

    Stupid employees interrupting me when they KNOW I’m busy giving my unasked for opinions over the intarwebs!

    2nd paragraph, 2nd sentence, it should be ‘do’ not ‘due’.

    And last bit, I’m talking about the press release, not your blog, when I reference the ‘denigrating statement’. Read a bit unclear who I was referring to in my eyes. :)

  4. You say the Japanese pointed the “massive 8.2 meter Subaru telescope” at this star? That’s surprising. I’ve always considered Subaru telescopes to be compacts, though quite good in the snow.

  5. Yes, I listened to the podcast of the 55 Cancri fifth planet press conference, and some of the journalists were asking ‘but haven’t we seen it all before?’ because of the hype around the previous exoplanetary finding, Gliese 581c. It was interesting listening to the scientists scrambling to put Gliese 581 in context without rubbishing their colleagues or downplaying their own findings.

  6. Michael Lonergan

    Lugosi, I wonder when the “Big Three”, GM, Ford and Chrysler are going to start manufacturing telescopes. I have yet to hear from Toyota and Honda, and how they plan to enter the telescope market.

  7. Gary Ansorge

    So, what’s the metal content of the star? Sol has one of the highest metal contents of our local (w/in 100 light years) group. That seems to say more about the likely formation of earth like planets than the total mass of the disk,,,

    GAry 7

  8. Ed Davies

    “It’s big in human terms, with a diameter 260 times the Earth-Sun distance….”

    The press release says it’s twice as big: that being the radius.

  9. Space Cadet

    Yes, it’s sensationalizing something fairly insignificant to make it sexy news. What else is new(s)?

    But I don’t see where they say that there ARE any planets forming there, just that their model suggests that earth-like planets are more likely than somewhere else to contain them. Pretty carefully worded. Like a campaign ad. I’m sure glad round one is finished here!

  10. Space Cadet

    more carefully worded than my offering! You get the picture, though.

  11. cc petersen

    I have done some work with the Subaru folk in the past (although not on THIS particular press release) and there are a few things to consider.

    They DO write their own press releases, usually in Japanese first. Then they get them translated. When I worked with them it was my job to straighten out the unclarities that result from the translation process into English. They mean well, and I’ve learned enough from it to see where things like this could creep in.

    I suspect that the error lies in that process, not (as some of you like to jump to conclusions about) that somebody in the PR office forced this on them. I’ve seen far worse things come through in first draft, usually as the result of someone trying to draw an analogy or an inference and the language just didn’t support it.

    Not sure what the process was for this one, but I’d cut ’em a little slack here. Not everything can be blamed on PR or “sexing up” a headline.


  12. Quiet Desperation

    I see Jesus!!!!!!

  13. Michael Lonergan

    QD, you took the words out of my mouth! If you look REAL close, he’s brandishing a huge club!

    I’m hitting the spam filter still :(

  14. bassmanpete

    Isn’t it misleading anyway to say Earth-like? Wouldn’t Earth-sized be more appropriate? To me, Earth-like means having an atmosphere, liquid water, etc. Venus is roughly Earth-sized but is hardly Earth-like. Not being an astronomer, tell me if I’m wrong on this – but do it nicely please :)

  15. To me, Earth-like means “overrun with superstitious, psychopathic creatures who have an abundance of weapons, used primarily on each other”

  16. You people seeing Jesus in that thing are nuts…. That’s clearly the Virgin Mary.

  17. Kaptain K

    Damn, bassmanpete beat me to it! Even if an Earth-sized planet forms there, there is no way it is going to be Earth-like! The habitable zone of an M5 dwarf is much smaller than Mercury’s orbit. Any planet would have a “year” measured in days and would be tidally locked in orbital resonance.

  18. StevoR

    Maybe they just don’t consider brown dwarfs count as stars? 😉

  19. StevoR

    After all, technically aren’t brown dwarfs neither quite stars nor quite planets butsomething in-between the twain?

    Stars can fuse hydrogen and sustain reactions -even tehdimmestand leasymassive -but brown dwrafs can only shrink, fuse a small amount of deuterium perhaps then shiut down forever …

    Superjovian planets – up to 80 x Jove if I recall right – are similar but can’t even manage to fuse deuterium … although there may be some overlap?

    So we sometimes call brown dwarfs “stars” (even giving them spectral classes – L &T ) but they’re actually not – instead being either “failed stars” or “really successful Jupiters” depending on how you look at it…

    Isn’t that right … ?

  20. Car jokers: Next time you see a Subaru car, look at the emblem- you will notice a pattern of stars.

    Subaru is the Japanese name for a constellation- guess which one from the auto emblem…

    As for Earth-like, I agree with bassmanpete, with the added caveat that since Earth took 30-50 million years to accrete, you can’t have an Earth-like planet in a disk that young.

  21. StevoR

    Well not yet anyway … 😉

    Ge it a few hundred million years though & you may have something habitable in places if not exactly like Earth …

  22. StevoR

    That’s supposed to read “*Give* it a few hundred million years though ..” of course. Sigh.

  23. How would you feel if someone living around this star (say on planet gorp-9, the Appalachian trail planet) called our Sun “a G2V or Fatty Fat Fat Fat star”? Don’t call stars dinky, call them petite. We all know, the Sun is not fat, just Big hydrogen’d.

  24. Christine P.

    I’m glad I’m not the only one who groaned at that press release! I hope Ms. Petersen is right and it was a matter of translation, not a deliberate attempt to overhype a finding. We PR folks have enough of a challenge balancing scientists vs public as it is!

  25. Tom Marking

    First of all, where did this abbreviation of the constellation to three letters come from? FN Tau? Isn’t it supposed to be FN Tauri?

    Second of all, if the disk contains 0.01 solar masses then that’s still 10.5 Jupiter masses so I don’t know why they would claim that no Jupiter-sized planet could form in the system. That would only be true if more than 90 percent of the mass was somehow lost from the disk during planetary formation.

    I’m a little bit curious how they estimate the age of the disk to 100,000 years. What are the signs that it was recently formed?


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