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Waspie_Dwarf

Transiting Exoplanet with Longest Known Year

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Transiting Exoplanet with Longest Known Year

Cambridge, MA - Astronomers have discovered a transiting exoplanet with the longest known year. Kepler-421b circles its star once every 704 days. In comparison, Mars orbits our Sun once every 780 days. Most of the 1,800-plus exoplanets discovered to date are much closer to their stars and have much shorter orbital periods.

"Finding Kepler-421b was a stroke of luck," says lead author David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA). "The farther a planet is from its star, the less likely it is to transit the star from Earth's point of view. It has to line up just right."

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Posted (edited)

QUOTE-

"The farther a planet is from its star, the less likely it is to transit the star from Earth's point of view. It has to line up just right."

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i'd have thought it was the plane that counted, not the distance?

if you're viewing it from the top down, it won't transit, but if you view it along the orbital plane, it would....

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Edited by shrooma

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i'd have thought it was the plane that counted, not the distance?

if you're viewing it from the top down, it won't transit, but if you view it along the orbital plane, it would....

The easiest way for me to explain this is with a diagram.

d40a14.jpg

In this diagram we are viewing a solar system side on (and obviously not to scale).

Both planet A and planet B orbit their star with the same inclination (i.e. they orbit in the same plane). However A, being closer to the star will transit from the point of view of an observer from Earth whereas B won't.

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The easiest way for me to explain this is with a diagram.

.

ta Waspie!

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QUOTE-

"The farther a planet is from its star, the less likely it is to transit the star from Earth's point of view. It has to line up just right."

.

i'd have thought it was the plane that counted, not the distance?

if you're viewing it from the top down, it won't transit, but if you view it along the orbital plane, it would....

.

I think "less likely" just means at any particular time, because it only comes around every 708 days.

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The easiest way for me to explain this is with a diagram.

d40a14.jpg

In this diagram we are viewing a solar system side on (and obviously not to scale).

Both planet A and planet B orbit their star with the same inclination (i.e. they orbit in the same plane). However A, being closer to the star will transit from the point of view of an observer from Earth whereas B won't.

But wouldn't Earth and planet A be on the same plane?

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But wouldn't Earth and planet A be on the same plane?

Their orbital planes are not the same.

You could argue that they are in the same orbital plane ONLY when the planet is transiting the star (and half an orbit later when the planet is behind the star from Earth's pov).

Look at the diagram. The line on which I have drawn planets A and B represents the orbital plane of the planets. It is inclined with respect to the Earth. When A transits the star it, the star and the Earth are all in a straight line, at other times they are not.

Planet B is in the same orbital plane as planet A but, because it is further from the star it always passes above or below the star from Earth's pov.

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Their orbital planes are not the same.

You could argue that they are in the same orbital plane ONLY when the planet is transiting the star (and half an orbit later when the planet is behind the star from Earth's pov).

Look at the diagram. The line on which I have drawn planets A and B represents the orbital plane of the planets. It is inclined with respect to the Earth. When A transits the star it, the star and the Earth are all in a straight line, at other times they are not.

Planet B is in the same orbital plane as planet A but, because it is further from the star it always passes above or below the star from Earth's pov.

Thanks Waspie, what I should have said tat the two are on the same geometric plane we we can see it and only then. I didn't mean to infer Earth and plant A orbitted at the same plane realative to their suns.

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Exoplanets, fascinating stuff.

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