5 ms·
Time to link one of my favorite plots currently: Orbital period vs mass distribution of known exoplanets: https://exoplanetarchive.ipac.caltech.edu/exoplanetp
by 7373737373 3y ago
Time to link one of my favorite plots currently:
Orbital period vs mass distribution of known exoplanets:
https://exoplanetarchive.ipac.caltech.edu/exoplanetplots/ https://exoplanetarchive.ipac.caltech.edu/exoplanetplots/
As you can see there, the type of exoplanet humanity has detected the most are Jupiter-sized exoplanets orbiting close to their stars.
For two reasons:
High masses aid the radial velocity method because they make their host stars wobble more compared to lower mass exoplanets. Lower mass wobbles are just outside the sensitivity range of our best spectrometers.
Also aiding in the transit method, they have a short "year" - typically just a few days, making them pass in front of their star more often. The likelihood of detecting these is therefore a lot higher during a given observation time. In addition, exoplanets that orbit more distantly from their star have a lower chance of having an aligned orbital plane, that makes them transit the star through our line of sight to it. The necessary angle of alignment is much tighter compared to closer orbiting exoplanets.
Earth-like exoplanets (~0.003 Jupiter masses, period= ~365 days) are currently outside the sensitivity range of most instruments. Jupiter-like exoplanets tend to reduce the brightness of their host star by at most a few % when they occlude it - Earth has about a tenth of the diameter of Jupiter, so less than 1/100th of its disk area, so when an exoplanet like it passes in front of a star, it only reduces its brightness by a one hundredth of these few percent.
This is where even 16-bit cameras cease to be useful because even if the exposure times are optimized to be as close as possible to filling their "photon count buckets" in a single exposure, Earth and exoplanets like it would only reduce the brightness by 6 instead of 655 (of 2^16=65536) counts, which isn't that statistically meaningful anymore with all the additional uncertainty that is involved when taking images.
- MeteorMarc 3y agoIf I follow your argument about 16 bit cameras, why are hundreds of earth sized planets detected with the transit method? (< 2R)
- 7373737373 3y agoI have no idea how, and would like to know. It may be that these are stars with smaller diameters, so the smaller planets occlude a larger fraction compared to sun-like stars. Otherwise I suspect the required hardware is likely out of reach for amateurs with current technology. Edit: Found these: https://en.wikipedia.org/wiki/MEarth_Project https://en.wikipedia.org/wiki/MEarth_Project > The MEarth Project is a United States NSF-funded, robotic observatory that is part of Fred Lawrence Whipple Observatory on Mt. Hopkins, Arizona, US. The project monitors the brightness of thousands of red dwarf stars with the goal of finding transiting planets. As red dwarf stars are small, any transiting planet blocks a larger proportion of starlight than transits around a Sun-like star would. This allows smaller planets to be detected through ground-based observations. https://www.eso.org/public/teles-instr/paranal-observatory/speculoos/ https://www.eso.org/public/teles-instr/paranal-observatory/s... > The mission for SPECULOOS is to detect terrestrial planets as they transit across small, cool stars in the solar neighbourhood It seems the terrestrial planets https://en.wikipedia.org/wiki/TRAPPIST https://en.wikipedia.org/wiki/TRAPPIST detected are also around dwarf stars. So I guess the summary is: finding and detecting earth-like planets around dwarf stars is possible, however around sun-like stars not quite yet using these two methods
- rich_sasha 3y agoI suppose it depends how regular the signal is otherwise. If a dip happens super-regularly (which I guess it would with single star planet orbits), it might be small relative to pointwise noise of the detector, but large enough to be detected over time (if you have the observations). Your point on period length stands. And anyway I'm just waxing lyrical, I'm a statistician and amateur stargazer not a pro :)
- pfdietz 3y agoHow often is the bucket filled during the transit? Noise in each emptying will average out, so a dip could be detected even if the dip in a single reading of the bucket could not be.
- 7373737373 3y agoTypical transits last a few hours, and exposures times are typically a few minutes. So you have up to hundreds of exposures per transit. I guess how "statistically recoverable" this data is depends beside the resolution also on the noise level. The atmosphere introduces a lot of variability in ground-based observations, and a star's brightness is not constant either.
- 7373737373 3y agohttps://astronomy.stackexchange.com/questions/51679/feasibility-of-detecting-earth-like-exoplanets-with-amateur-telescopes https://astronomy.stackexchange.com/questions/51679/feasibil...
- inoop 3y agoDamn those are some good names
- hotpotamus 3y agoYeah, I was going to say it's probably to do with "sun-like" and angular size ratios. (I'm not religious, but the sun and the moon being the same angular size has always felt like an easter egg that a creator might leave as a bit of fun). Sun-like is important in the search for life because despite putting out lots more energy, the suspicion is that yellow stars tend to be less temperamental in their flare behavior (so they don't scour the surface of any potential planets with large amounts of radiation every once in awhile). And there is evidence that our sun is even a particularly calm yellow star. The habitable zone is also in a region that doesn't tidally lock the planet; a day-night cycle seems important though not neccesarily a requirement for habitability. And yellow stars' lifecycle seems to be long enough to allow for life to form and evolve. Essentially they seem most likely to produce habitable planets - it's probably not mere happenstance that we live around one.
- contravariant 3y agoTake measurements across multiple transits and average them. Periodic signals are quite easy to identify even amongst noise.
- 7373737373 3y agoIn the case of an earth-like planet (considering not just composition and size, but also orbit + host star similarity) that's difficult to do when the transit only occurs every 365 days Even finding just one such planet will require a lot of observation: The "geometric probability" of the orbital plane being aligned for an earth-like orbit seems to be around 0.5% [0]. Assuming every star has an earthlike planet [1], only 1 in 200 observed stars will be correctly aligned. So observing 365*200=73,000 stars over an entire day (also not possible for ground-based telescopes due to the day/night cycle) should statistically result in one transit observation. The transit duration is also a problem, for an earth-like exoplanet it is 13 hours, so if the observation time is too short, one would only catch the beginning or end of the transit [0] https://www.researchgate.net/figure/Transit-Properties-for-Solar-System-Objects_tbl1_226590554 https://www.researchgate.net/figure/Transit-Properties-for-S... [1] The current hypothesis seems to be that every star has at least one planet https://en.wikipedia.org/wiki/Planet-hosting_star https://en.wikipedia.org/wiki/Planet-hosting_star), but it's all a bit up in the air as not many exoplanets (and especially earth-like ones) have been observed yet. The sample size is too low.
- zuminator 3y ago> The current hypothesis seems to be that every star has at least one planet I think you mean, that stars have at least one planet on average. E.g. in the unlikely event that only one third of stars had planets, but each one of those stars had on average 3 stars, then it would fit the hypothesis of averaging at least one planet per star. It's not a stretch at all since our rather boring star has at least 8 planets, and of the 4,051 stars we can currently detect with exoplanets, they have a total of 5,438 planets, meaning over 1.34 planets per star not including the unknown but unquestionably vast number of planets we currently don't have the capability of detecting. Still, just as we suspect large numbers of rogue planets that have lost their stars, there must be at least some stars out there that have lost their planets, whether to passing neutron stars or perhaps indigestion. [0] https://en.wikipedia.org/wiki/Lists_of_exoplanets#:~:text=These%20are%20,systems https://en.wikipedia.org/wiki/Lists_of_exoplanets#:~:text=Th...
- rbanffy 3y agoWhat I like the most in finding gas giants is that each of them must come with a full compliment of rocky or icy moons, which is wonderful news for anyone looking for life similar to ours.
- monocasa 3y agoMust they? Depending on where the original atoms of the start system in question are in their journey through the eons, there might not be a lot of rocky material at all in a given system.
- hinkley 3y agoMy somewhat limited understanding of astrophysics is that the source material for the solar system dictates what class of star can form. Supernovas create a certain range of star types and also produce heavy atomic weights.
- rbanffy 3y agoIndeed. You'd only expect to find rocky planets and satellites around high metallicity stars. Still, gas giants in one of those Goldilocks zone may have a lot of prime real estate.
- deleted 3y ago[deleted]