Earth sized rocky exoplanets

I wondered the same things. Is the dip in energy when a planet that is a small fraction on the size of the star large enough to be statistically significant? They might have worked it out, but a cluster of asteroids could cause the same dip, and a smaller body getting in the way between there and here could do the same.

I don't think they're ruling all other possibilities out, in terms of certainties. I think they're talking probabilities.

One of the major things to understand about the search for exoplanets, and one I've yet to see explained in any popular science journalism about the subject, is the extreme limitations of the methods used to detect exoplanets. First, in order to detect dips in stellar brightness, two major things need to exist:

1. The planetary orbits around stars need to be oriented edge-on to us.

2. The orbiting planets need to circle very close to the star, so that we see the dip in brightness with some predictable regularity.

What these two things mean is that if our star were being viewed by some extra-solar alien astronomers, it is very unlikely that they would detect any planets via this method.

Stellar "wobble", that the very slight motion of the star in response to a planetary gravitational pull, is another method used to detect extrasolar planets, and will work regardless of the orbital orientation, but you need a big planet orbiting close to the star, regardless. Again, this wouldn't allow detection of our solar system from any distant star. The nearest big planet to our sun is Jupiter, which orbits ever 12 earth-years, and is so far from the star that its gravitational disturbance would likely be undetectable.

Bottom line being, there are probably oodles of stellar planetary systems out there, including very near ones, which we still don't have the technology to detect. That's the bad news.

The good news is that the advancement in extrasolar planetary detection has been so rapid that we can expect ever more fascinating discoveries in the very near future.

caw

Snick said:

I wondered the same things. Is the dip in energy when a planet that is a small fraction on the size of the star large enough to be statistically significant? They might have worked it out, but a cluster of asteroids could cause the same dip, and a smaller body getting in the way between there and here could do the same.

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They watch the star for many, many orbits to get good statistics. It's actually pretty awesome; they can rule out even variations due to sunspot activity.

If the armada of starships is in orbit around the star, I don't think they could tell the difference between it and a planet, although the ships would have to be pretty densely packed to register. We can't yet detect an asteroid belt around another star, for example. Even finding Earth-sized objects is still pretty tricky.

blacbird said:

...
Bottom line being, there are probably oodles of stellar planetary systems out there, including very near ones, which we still don't have the technology to detect. That's the bad news.

Click to expand...

That's BAD news? As in aliens could show up and we wouldn't know where they came from?

The good news is that the advancement in extrasolar planetary detection has been so rapid that we can expect ever more fascinating discoveries in the very near future.

caw

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I'm guessing the James Webb Space Telescope will help. It looks like funding is still alive, after the threat to kill it last summer.

jjdebenedictis said:

They watch the star for many, many orbits to get good statistics. It's actually pretty awesome; they can rule out even variations due to sunspot activity.

Click to expand...

That would have to be a lot of good statistics. I saw a transit of Mercury circa 1969 (my father had a 4-inch reflector he used to project the Sun's image on a piece of paper), it was barely visible black dot in the 6-inch diameter image of the Sun. If I hadn't seen it move across the face of the Sun from minute to minute, I might not have noticed or recognized it, thinking it was either a very small sunspot or a speck of something on the paper.

Mercury is 3,000 miles in diameter vs. the Sun's 870,000 miles diameter. That's about a 200 to 1 diameter difference, and 40,000 to 1 area difference, so the Sun's light drops about 1 part in 40,000 with a Mercury transit. Earth may have 10 times the area, but that's still a really small drop in brightness to be able to detect. No doubt t would take many orbits (meaning many years of observation, including that unknown hour or so of the transit) to get reasonable data. I've seen how DSP can be used to to get very low-level signals from noise, but this looks to be on the edge of technology.

NOW let me read the article....

Compared with Earth’s leisurely 365-day orbit, the new planets practically whiz around their star in a matter of days or weeks.

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Yeah, that would help get more info quicker.

benbradley said:

Yeah, that would help get more info quicker.

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Oh, yes! There's a reason why so many of the exoplanets they discover are either lumbering behemoths or rillyrillyrilly close to the star. It will take a few years of steady data-taking before they'll be able to report on exoplanets that are more like Earth in terms of size and orbit.

benbradley said:

Mercury is 3,000 miles in diameter vs. the Sun's 870,000 miles diameter. That's about a 200 to 1 diameter difference, and 40,000 to 1 area difference, so the Sun's light drops about 1 part in 40,000 with a Mercury transit. Earth may have 10 times the area, but that's still a really small drop in brightness to be able to detect.

Click to expand...

So far no exoplanet as small as Mercury has been detected, and possibly none as small as Earth, for precisely this reason. Most detected exoplanets are "hot Jupiters", gas giants orbiting very close to their suns, with periods of as little as three days.

Geometry gets involved here. A planet orbiting very close to its sun has a much better chance of being detected because it can eclipse the sun at a wider orbital angle and still be detected. A planet orbiting a long way from its sun will both have a much longer orbital period (Jupiter's is twelve Earth years), but also has a far smaller chance of being aligned at just the right orbital angle relative to us to eclipse the star.

That may seem elementary and obvious, but it seems also to have escaped the notice of every popular science article I've ever read on the subject of extrasolar planet detection.

caw