<p><a href="https://arxiv.org/abs/1912.01821v1" rel="nofollow noreferrer">A recent study</a> indicates that Cold Jupiters similar to Saturn and Jupiter greatly outnumber Hot Jupiters. The authors studied 18 years worth of data to find long-period exoplanets, that is planets far from their host star. </p>

<p>Cold Jupiters, being farther from their host star, have longer periods than Hot Jupiters. Therefore, they need to be observed over a longer time frame to see multiple transits. ETs would need to observe the Sun for 12 years before seeing two transits of Jupiter, and that still wouldn't be enough to confirm its presence.  </p>

<p>Planets that are further out also induce smaller variations in the velocity of their host star, so the spectrum of the star is shifted by a smaller amount. Therefore higher resolution spectrographs are needed to detect Cold Jupiters using the radial velocity method. </p>

<p>Finding more Warm and Hot Jupiters at the beginning of the era of exoplanetary discovery was an observational bias due to the limits of the instrumentation available at the time, and the amount of time needed to find long-period exoplanets. </p>

CC BY-SA 4.0
2019-12-05T21:13:16.843Z
Is this because the closer a planet is to the star, the more regular the dips and thus easier to be detected? Something like Jupiter only dips in front of the Sun once every 12 years, so it only would have been seen once or twice since we found our first ever exoplanet in 1995 - very difficult to draw a conclusion from that!!
corsiKa
CC BY-SA 4.0
2019-12-06T00:49:54.507Z
@corsiKa, it's because most exoplanet-detection methods require you to watch the parent star for one full period of the planet's orbit.  To detect Jupiter, you need to watch the Sun for 12 years.
Mark
CC BY-SA 4.0
2019-12-06T18:04:50.897Z
@usernumber (and Mark) Actually, for transit you need at least three of them. When you see 2 dips, there's still no way to know whether those 2 dips were different planets, maybe 2 transits of something else entirely (possibly a solar system object), etc. Only with 3 transits you get 2 intervals, meaning you can confidently tell there is some rythm.
Emil Bode
CC BY-SA 4.0
2019-12-06T18:09:46.903Z
Also, even for spectroscopy you need to be able to see some *change*. Just seeing a star move doesn't tell us anything, stars have all kinds of motions. Only when you can see there is some pattern to the movement, can you conclude there is a planet.
Emil Bode
CC BY-SA 4.0
2020-02-18T16:44:28.813Z
There is in fact no problem with radial velocity precision in finding cold Jupiters, only an issue in observing the target for more than one orbital period. Present levels of RV precision are an order of magnitude or more smaller than the RV variations induced by a Jupiter-like planet in a Jupiter-like orbit around a sun-like star.
ProfRob
CC BY-SA 4.0
2019-12-05T10:07:12.760Z
2019-12-09T08:43:30.453Z
2019-12-09T08:43:30.453Z
usernumber
<p>I remember a few years ago hearing that Jupiter was an anomaly in the landscape of exoplanets. Back then, most Jupiter-mass planets discovered were Hot Jupiters, orbiting very close to their host star. </p>

<p>In the last few years since I heard this, many new exoplanets have been discovered. Do we know now if there are many more Hot Jupiters and our own Jupiter is a rather rare occurrence, or if this was an observational bias and there are many more "Cold Jupiters"?</p>

CC BY-SA 4.0
2019-12-05T22:31:15.680Z
Jupiter is a possible solution to the Fermi Paradox, the rare Earth hypothesis. https://en.wikipedia.org/wiki/Rare_Earth_hypothesis#The_right_arrangement_of_planets It's hypothesized that Jupiter protects Earth from comets by sweeping up stray debris with its large gravitational field. Along with a big moon and a few other attributes.
Chloe
CC BY-SA 4.0
2019-12-06T10:08:15.620Z
Note that all else equal, Hot Jupiters will be much easier to find than Cold Jupiters, using the techniques we use to observe planets in other solar systems. This is a common problem in astronomy :)
Luaan
<exoplanet><hot-jupiter><cold-jupiter>
Is Jupiter still an anomaly?
usernumber
# Is Jupiter still an anomaly?

(Asked by: username_0 on 2019-12-05)

I remember a few years ago hearing that Jupiter was an anomaly in the landscape of exoplanets. Back then, most Jupiter-mass planets discovered were Hot Jupiters, orbiting very close to their host star.

In the last few years since I heard this, many new exoplanets have been discovered. Do we know now if there are many more Hot Jupiters and our own Jupiter is a rather rare occurrence, or if this was an observational bias and there are many more "Cold Jupiters"?

**Tags:** exoplanet, hot-jupiter, cold-jupiter

> **Comments:**
> **username_1**: Jupiter is a possible solution to the Fermi Paradox, the rare Earth hypothesis. https://en.wikipedia.org/wiki/Rare_Earth_hypothesis#The_right_arrangement_of_planets It's hypothesized that Jupiter protects Earth from comets by sweeping up stray debris with its large gravitational field. Along with a big moon and a few other attributes.  
> **username_2**: Note that all else equal, Hot Jupiters will be much easier to find than Cold Jupiters, using the techniques we use to observe planets in other solar systems. This is a common problem in astronomy :)  

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## 1 answers

### Answer by username_0 on 2019-12-05. Score: 31

[A recent study](https://arxiv.org/abs/1912.01821v1) indicates that Cold Jupiters similar to Saturn and Jupiter greatly outnumber Hot Jupiters. The authors studied 18 years worth of data to find long-period exoplanets, that is planets far from their host star.

Cold Jupiters, being farther from their host star, have longer periods than Hot Jupiters. Therefore, they need to be observed over a longer time frame to see multiple transits. ETs would need to observe the Sun for 12 years before seeing two transits of Jupiter, and that still wouldn't be enough to confirm its presence.

Planets that are further out also induce smaller variations in the velocity of their host star, so the spectrum of the star is shifted by a smaller amount. Therefore higher resolution spectrographs are needed to detect Cold Jupiters using the radial velocity method.

Finding more Warm and Hot Jupiters at the beginning of the era of exoplanetary discovery was an observational bias due to the limits of the instrumentation available at the time, and the amount of time needed to find long-period exoplanets.

> **Comments:**
> **username_3**: Is this because the closer a planet is to the star, the more regular the dips and thus easier to be detected? Something like Jupiter only dips in front of the Sun once every 12 years, so it only would have been seen once or twice since we found our first ever exoplanet in 1995 - very difficult to draw a conclusion from that!!  
> **username_4**: @username_3, it's because most exoplanet-detection methods require you to watch the parent star for one full period of the planet's orbit.  To detect Jupiter, you need to watch the Sun for 12 years.  
> **username_5**: @username_0 (and username_4) Actually, for transit you need at least three of them. When you see 2 dips, there's still no way to know whether those 2 dips were different planets, maybe 2 transits of something else entirely (possibly a solar system object), etc. Only with 3 transits you get 2 intervals, meaning you can confidently tell there is some rythm.  
> **username_5**: Also, even for spectroscopy you need to be able to see some *change*. Just seeing a star move doesn't tell us anything, stars have all kinds of motions. Only when you can see there is some pattern to the movement, can you conclude there is a planet.  
> **username_6**: There is in fact no problem with radial velocity precision in finding cold Jupiters, only an issue in observing the target for more than one orbital period. Present levels of RV precision are an order of magnitude or more smaller than the RV variations induced by a Jupiter-like planet in a Jupiter-like orbit around a sun-like star.  

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