A Four Planet System in Orbit, Directly Imaged and Remarkable | Hacker News Reader

A Four Planet System in Orbit, Directly Imaged and Remarkable

astrobiology.nasa.gov

226 pointskilovoltaire12 comments

This article neatly illustrates something I find interesting: the biases of the various methods of detecting exoplanets.

https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...

Direct imaging more easily detects massive planets that orbit far away from their star. Every one of the planets that orbit HR8799 (that we've detected) are farther out than Saturn, and many times heavier than Jupiter.

On the other hand, the transit and and radial velocity methods work better for planets that are closer to their star, and with radial planes that are edge on to us. On the third hand, with the astromery method, it helps for the orbital plane to be face on to us, so we can detect the wobble in the host star!

For all these methods, it helps if the star is both small and dim. The only way we'll find out if Rigel A (~120,000x brighter than Sol) hosts a planet is if we send a probe there.

>On the third hand...

Sounds these biases on exoplanets hit a little too close to home.

If it matters to you, you are not actually seeing the planets in motion:

> Wang said that the animation is based on eight observations of the planets since 2009. He then used a motion interpolation algorithm to draw the orbit between those points.

I wish NASA was more upfront with the enhancements it adds to media, including often adding color and, in this case at least, adding motion.

Hmm, I think the projection of an ellipse in perspective is still an ellipse. Do we know if these 8 data points were enough to determine whether the planets are all orbiting roughly on the same plane, as in the Solar system?

Sort of. Add knowledge of Kepler's second law that an orbit will sweep out equal area in equal time, and you'll find that you can tell how much the orbit has been rotated, but not in which direction. I think generically, you'll find four possible orientations for a given projection. If you have multiple planets, and all planets share a particular possible elliptical plane, you might guess they're all on that plane, but it could be a coincidence.

OK, you clearly did not read the article because you are incorrect.

That statement you quote is referring to the still image in the article, below the video, which is of an entirely different star and system of planets (Fomahault b).

The video has a time legend /embedded in the movie/, at the bottom of the frame clearly showing when the observation for each frame of the video was taken.

NASA was being plenty up front here, I think you maybe just skimmed the article slightly too quickly.

No, he is correct. Eight of the frames in the animation are real observations. Between these eight frames, the other frames are interpolated.

Read more carefully - HR8799 is the subject of the animation up top, and the subject of the quote about motion interpolation. Both are credited to J. Wang, while the composite photo of Fomahault B is credited elsewhere. Also note the use of the term 'animation', and that he refers to images taken since 2009 (whereas the Fomahault B images start in 2004).

Is it correct to say this kind of direct imaging only works if the planets are large and hot enough to have a significant infrared output of their own, rather than light reflected from their star?

> HR 8799 is 129 light years away

i know pretty much nothing about astronomy, which is probably why i find it amazing that this planet-level imagery was collected by an earth-based telescope. fantastic work.

i can't help but wonder: will we see more imagery/animations of other exoplanets in the near future or is this just a rarity?

Might not be the coolest plateary system we'll ever spot but I'm glad to have lived to see the first.

Yep, the Warden Diamond has been verified (https://en.wikipedia.org/wiki/Four_Lords_of_the_Diamond)! Very imaginative and gripping series that I totally recommend.

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