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Astronomers Determine the Length of Day of an Exoplanet34

The Bad Astronomer writes: "Astronomers have just announced that the exoplanet Beta Pic b — a 10-Jupiter-mass world 60 light years away — rotates in about 8 hours. Using a high-resolution spectrometer and exploiting the Doppler shift of light seen as the planet spins, they measured its rotation velocity as 28,000 mph. Making reasonable assumptions about the planet's size, that gives the length of its day. This is the first time such a measurement has been achieved for an exoplanet."
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Astronomers Determine the Length of Day of an Exoplanet

• But have they determined the length of its week? (Score:3)

on Wednesday April 30, 2014 @04:13PM (#46883423)
I mean, we need to know when to schedule parties.
• smallprint (Score:1)

7 hours in the mountain and central tz.
• Re: (Score:2)

Only 6 on the west coast.
• Big deal (Score:1)

Day length can amount to half a year on good old Earth.

• Derived Properties of the Planet (Score:4, Informative)

on Wednesday April 30, 2014 @04:42PM (#46883719)

You can calculate a lot from this information. From the rotation period and velocity we get a radius of 57,000 km, and an equatorial rotation velocity of 12.5 km/s.

From the mass we get a surface gravity of 389.6 m/s^2 (about 40 g's), but the centrifugal acceleration from rotation is -2.74 m/s^2. Thus the body would not be flattened as much as Jupiter. The density is about 24,500 kg/m^3, higher than Osmium. Iron at the core of a planet is quite compressible, so for a large body such as this, it can give such a high density.

• Circular planets, circular reasoning (Score:2)

Are you sure none of what you just derived wasn't what lead up
to their 28,000 mph in the first place?

On a side note: are universal distances measured in miles?
I think not.

• Re: (Score:3)

Are you sure none of what you just derived wasn't what lead up
to their 28,000 mph in the first place?

It goes further!
From the rotation period, radius and equatorial rotation velocity, we get pi = 3.1578947 and 1 mile = 1.6071429 km

• Re: (Score:1)

by Anonymous Coward
How can you do what you are doing? TFS says they made reasonable assumptions about the planets size to calculate the length of its day. You can't take those results and use them to calculate the exact size of the planet. Shit doesn't work like that. It's like like using 3 as an approximate value for pi, calculating the area of a circle, and then using the calculated area of the circle to figure out pi and declare it to be precisely 3.0000.
• At what point is it a star? (Score:5, Informative)

on Wednesday April 30, 2014 @04:49PM (#46883805)

Beta Pic b — a 10-Jupiter-mass world

How is that not a star?
I thought Jupiter was half-way to critical mass where it all explodes into a fireball?

Searching...

Nope. I was wrong. Jupiter would need about 75 times more mass before it went nuclear, fused hydrogen at it's core and became a star. A 10-Jupiter mass planet is totally legit.

• How does the rotation speed affect gravity? (Score:1)

How does the rotation affect the gravity of a planet?
If the planet is rotating fast enough, does that reduce the force of gravity, or does the gravity still 'squash' you since it is actually affecting the space around it.

For example, if there was a planet with twice the mass of Earth, but spinning twice as fast, what would it be like to stand on the surface?

Do black holes spin? -or are they 'locked in' because the mass would be impossible to move.

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