APOD: HR 8799: Multi-planet Star System (2008 Nov 17)

[bystander]

Most of us probably knew about this Friday, Nov 14, but is good to see anyway.

http://apod.nasa.gov/apod/ap081117.html

Here's some news releases from Thursday.

Extrasolar planetary system makes pictorial debut
ScienceNews - November 13, 2008

First images of planetary system beyond the solar system released

Astronomers capture first images of newly discovered solar system
Provided by Lawrence Livermore National Laboratory
Astronomy.com - November 13, 2008

A team of researchers was able to see three orbiting planetary companions to HR8799 using high-contrast, near-infrared adaptive optics observations.

Major Breakthrough: First Photos of Planets Around Other Stars
Space.com - November 13, 2008

Astronomers have taken what they say are the first-ever direct images of planets outside of our solar system, including a visible-light snapshot of a single-planet system and an infrared picture of a multiple-planet system.

[orin stepanek]

Could there be maybe some smaller planets hidden in the stellar glare? Even the innermost planet is like Neptune's orbit. Makes you wonder: - - What's out there?

Orin

[neufer]

Could there be maybe some smaller planets hidden in the stellar glare?
Even the innermost planet is like Neptune's orbit.
Makes you wonder: - - What's out there? Orin

http://exoplanet.eu/planet.php?p1=HR+8799&p2=b
http://exoplanet.eu/planet.php?p1=HR+8799&p2=c
http://exoplanet.eu/planet.php?p1=HR+8799&p2=d
--------------------------------------------------
Planet : HR 8799 b Dist. (proj.)_ ~10 + 56 AU
Planet : HR 8799 c Dist. (proj.)__ 10 + 28 AU
Planet : HR 8799 d Dist. (proj.)__ 10 + 14 AU
..............................................
"Bodes Law" ~ 10 + 14 * (2 ^ b) AU
..............................................
{Inner most Planet : HR 8799 e Dist. (proj.)__ 10 AU

[saberard]

"...it is a clear demonstration that complex planetary systems exists..."

No comment.

[Moonshadow]

Pretty cool!

It seems (from a back of an envelope calculation) that the apparent diameter of the planets (based on their angular sizes) is about 2000 times that of Jupiter.

This seems rather large. Could this be due to the resolution of the image?

[apodman]

"...it is a clear demonstration that complex planetary systems exists..."

No comment.

It's exo-syntax. As we explore the universe, let us remember to be culturally tolerant.

[saberard]

Aha! Romulan grammar then!

[Colorado Fred]

Wikipedia has a nice article on HR 8799 and its planets. It states the planets are about 3X, 10X, and 10X Jupiter masses, with very large orbits with unknown configurations. I get excited every time one of these news releases comes out only to find Earth and our Solar system continue to be unique. About 300 stars have been examined with 85% having a total of over 300 planets. I assume it might be an even higher percentage except the doppler method most often used doesn't work well if the system is viewed from a pole. Most of the systems are of super-Jupiter size planets in either very close near-circular or highly elliptical orbits, both of which preclude any possibility of inner, Earth-like planets. The only one (?) system coming close to matching our system has two possibly icy-dense water-rocky planets about 5X Earth masses.
I don't often find this sort of reality check in the press releases.

[Pete]

This discovery is awesome (as much as the Fomalhaut one). Nice going, scientists!

Pretty cool!

It seems (from a back of an envelope calculation) that the apparent diameter of the planets (based on their angular sizes) is about 2000 times that of Jupiter.

This seems rather large. Could this be due to the resolution of the image?

2000 Jupiter radii is about 2E3 * 7E7 m = 14E10 m, or 140 million km, a bit less than 1 AU ( = 150 million km). No main sequence star (let alone any planet) approaches that size. I'd guess that the point-like planet sources were smeared out by atmospheric seeing and imperfect adaptive (active?) optics.

The links Neufer posted give radius estimates for each of the planets (from innermost planet outward): 1.2, 1.2, 1.1 Jupiter radii. I ran some quick Swift simulations (pretty reliable symplectic method), and the orbits are unstable on a time scale of millions of years, even if the planet masses are halved. That's assuming circular orbits and zero initial inclination, which admittedly isn't realistic. I'm sure the pros have already been hard at work to say something about the planets' stability.

[BMAONE23]

How well does Mass equate with Gravity? If I, weighing roughly 200 lbs, were to be standing on a 5X earth mass super earth planet would i then weigh 1/2 ton?

[astrolabe]

Hello BMAONE23,

Sorry, too much caffeine, can't keep my fingures off the keyboard. The rewrites are killing me!

Maybe the question should be: "What would my diameter be?" It might be a good inquiry, though.

[neufer]

Could there be maybe some smaller planets hidden in the stellar glare?
Even the innermost planet is like Neptune's orbit.
Makes you wonder: - - What's out there? Orin

http://exoplanet.eu/planet.php?p1=HR+8799&p2=b
http://exoplanet.eu/planet.php?p1=HR+8799&p2=c
http://exoplanet.eu/planet.php?p1=HR+8799&p2=d
--------------------------------------------------
Planet : HR 8799 b Dist. (proj.)_ ~10 + 56 AU
Planet : HR 8799 c Dist. (proj.)__ 10 + 28 AU
Planet : HR 8799 d Dist. (proj.)__ 10 + 14 AU
..............................................
"Bodes Law" ~ 10 + 14 * (2 ^ b) AU
..............................................
{Inner most Planet : HR 8799 e Dist. (proj.)__ 10 AU

A better guess (perhaps):
--------------------------------------------------
Planet : HR 8799 b Dist. (proj.)__ 9 + 176/3 AU
Planet : HR 8799 c Dist. (proj.)__ 9 + 88/3 AU
Planet : HR 8799 d Dist. (proj.)__ 9 + 44/3 AU
..............................................
Planet : HR 8799 e Dist. (proj.)__ 9 + 22/3 AU
Planet : HR 8799 f Dist. (proj.)__ 9 + 11/3 AU
Planet : HR 8799 g Dist. (proj.)__ 9 + 11/6 AU
.
.
{Inner most Planet : HR 8799 ? Dist. (proj.)__ 9 AU

[astrolabe]

Hello BMAONE23,

How well does Mass equate with Gravity? If I, weighing roughly 200 lbs, were to be standing on a 5X earth mass super earth planet would i then weigh 1/2 ton?

Here's kind of a fun site:
http://www.exploratorium.edu/ronh/weight/

[apodman]

How well does Mass equate with Gravity? If I, weighing roughly 200 lbs, were to be standing on a 5X earth mass super earth planet would i then weigh 1/2 ton?

Maybe the question should be: "What would my diameter be?"

If a 200 lb. BMAONE23 stood on a 5x Earth-mass planet with the same diameter as Earth, he would weigh 1/2 ton (1000 pounds).

Consider this: Mercury has .055 of the mass of Earth, but divide .055 by the square of the ratio of their radii (divide by .146) to get a surface gravity for Mercury equal to .38 of Earth.

Consider this: Mars has .107 of the mass of the Earth, but divide .107 by the square of the ratio of their radii (divide by .284) to get a surface gravity for Mars equal to .38 of Earth.

Consider this: The ratio of the mass of Mars to the mass of Mercury (1.94:1) is approximately the square of the ratio of the radius of Mars to the radius of Mercury (1.39:1), so force of gravity is about the same on the surface of each.

The force of a planet's gravity on an object at a planet's surface is directly proportional to the planet's mass and inversely proportional to the square of its radius.

---

If your 5x Earth-mass planet had the same density as Earth, its radius would be the cube root of 5 (about 1.71) times Earth's radius. So start with 1, multiply by 5, divide by the square of 1.71, and you get a surface gravity of 1.71 times that of Earth. So an object or person weighing 200 lbs. on the surface of Earth weighs 342 pounds on this planet.

[orin stepanek]

The point I was trying to make was that if there were smaller planets they would be hidden in the glare of the star which was apparently blocked out, The innermost planet 'd' which is as far or further than the orbit of Neptune, You will notice that planet 'd' is shown at the edge of the blocked out area. It could also be that smaller planets around other stars are too close to the star and too difficult to be spotted with present methods of observation. Kepler which is to be launched next year may shed some new light on the planet search.

Orin