PDA

View Full Version : Three Neptunes Orbiting Another Star



Fraser
2006-May-19, 10:15 PM
SUMMARY: Astronomers have discovered a nearby star that's home to three Neptune-sized planets; no super-Jupiters here. The star, HD 69830, is located 41 light-years away in the constellation of Puppis. With magnitude 5.95, it's just possible to see with the unaided eye. The discovery was made using the European Southern Observatory's 3.6 metre telescope at La Silla in Chile. The planets orbit their star in 8.67, 31.6 and 197 days respectively.

View full article (http://www.universetoday.com/am/publish/trio_neptunes_belt.html)
What do you think about this story? post your comments below.

knealy
2006-May-21, 12:23 AM
Isn't this a bit of a problem to have a Neptune size planet orbit its star in 8 days? I thought it impossible for this size planet to be so close to its star.

Ilya
2006-May-21, 01:14 AM
Isn't this a bit of a problem to have a Neptune size planet orbit its star in 8 days? I thought it impossible for this size planet to be so close to its star.
Eleven years ago, everyone else thought so too. Not any more. Google "hot Jupiters".

Van Rijn
2006-May-21, 09:00 AM
Isn't this a bit of a problem to have a Neptune size planet orbit its star in 8 days? I thought it impossible for this size planet to be so close to its star.

There were a lot of ideas about planets. Another one was that Jupiter and Super Jupiter mass planets would be extremely rare. That's what's so great about finally being able to detect planets in other solar systems - we're learning what the real rules are, and finding that there are planets not quite like anything in our solar system.

altizar
2006-May-22, 03:12 PM
A little theoretical thinking here. The large neptune size planet was found in the habitable zone for a smaller sized star. Chances are since the star was smaller than the sun, it's solar winds are less than the suns. So I would think that means that this star wasn't able to push as much debris away during the formation period, thus allowing for the larger size development closer to the star. It would also explain the part of why you get gas giants far out and rocky ones in close. (sorry free thinking here not up on my planetary evolution info) Gas is easier to push than rock with solar winds.

As to the Jupiter size planets being rare, Jupiter is just a failed star or brown dwarf. For Jupiter to be a Rare occurence, it would imply to me that binary star systems would also have to be rare.

Mungascr
2006-May-24, 07:55 AM
'Altizar' good thinking : Smaller stars are also considerably dimmer with orangey-reddish light - at least when they're not flaring! Their habitable zone would be closer too. Protoplanetary disks of much smaller size have been found around brown dwarf stars and so that all makes sense.

Small nit-pick tho' - Jupiter is technically a gas giant planet not a brown dwarf. This is for two reasons :

I) Jupiter is just not massive enough. By my understanding, it needed to be at least eight times more massive to qualify. Some exoplanets (notably 70 Virginis-b +) may qualify for both (ie. the categories of 'Superjovian planet' and 'Brown dwarf' may overlap) but our Jove doesn't.

&

II) because it formed from a disk around our Sun instead of forming the way stars do from collapsing interstellar gas & dust clouds.

I'm being pedantic here I know but just thought I'd let you know. Besides I don't think of brown dwarfs as "failed stars" so much as "really, really, successful Jupiters" myself! ;-)

Thanks 'Fraser' for that - I hadn't yet heard & appreciated reading that.

N.B. Sorry folks but I still can't seem to get the bold thing working here.

Edited for usual typos & to add joke, joke warning & addendum.

knealy
2006-May-27, 01:15 AM
What about the tidal forces so close the its sun? It was my understanding that tidal differentials would rip apart large objects this close. Is this not a factor with gas giants because they are "viscous"?

PS. I'm not arguing against observation, only what I was led to believe.

antoniseb
2006-May-27, 06:26 PM
What about the tidal forces so close the its sun? It was my understanding that tidal differentials would rip apart large objects this close. Is this not a factor with gas giants because they are "viscous"?


No, gas giants would be the must vulnerable type of object to this tidal ripping inside the Roche limit. However, these planets are not nearly close enough to the star for the differential gravitation of the star to be stronger than the internal gravitation of the objects. On Earth, for example, that is the difference between the gravitational force we feel toward the Sun at noon compared to midnight? How does this compare to the force we feel toward the center of the planet? The differential gravitation is very small for here. I think the Earth would have to be actually well inside the Sun for the differential gravitation to tear it apart.