Planets around other stars are like peas in a pod

Posted: January 10, 2018 by oldbrew in Astrophysics, exploration, solar system dynamics
Tags: , ,

Jupiter-sized exoplanet [Wikipedia]

It seems the planetary structure of our solar system is an oddity compared to most of the exoplanetary systems so far discovered. On the other hand it’s easier to find planets close to their stars than those a long way away, so what is known so far might not be giving us the whole picture.

An international research team led by Université de Montréal astrophysicist Lauren Weiss has discovered that exoplanets orbiting the same star tend to have similar sizes and a regular orbital spacing, says

This pattern, revealed by new W. M. Keck Observatory observations of planetary systems discovered by the Kepler Telescope, could suggest that most planetary systems have a different formation history than the solar system.

Thanks in large part to the NASA Kepler Telescope, launched in 2009, many thousands of exoplanets are now known. This large sample allows researchers to not only study individual systems, but also to draw conclusions on planetary systems in general.

Dr. Weiss is part of the California Kepler Survey team, which used the W. M. Keck Observatory on Maunakea in Hawaii, to obtain high-resolution spectra of 1305 stars hosting 2025 transiting planets originally discovered by Kepler. From these spectra, they measured precise sizes of the stars and their planets.

In this new analysis led by Weiss and published in The Astronomical Journal, the team focused on 909 planets belonging to 355 multi-planet systems. These planets are mostly located between 1,000 and 4,000 light-years away from Earth.

Using a statistical analysis, the team found two surprising patterns. They found that exoplanets tend to be the same sizes as their neighbors. If one planet is small, the next planet around that same star is very likely to be small as well, and if one planet is big, the next is likely to be big. They also found that planets orbiting the same star tend to have a regular orbital spacing.

“The planets in a system tend to be the same size and regularly spaced, like peas in a pod. These patterns would not occur if the planet sizes or spacings were drawn at random”, explains Weiss.

The similar sizes and orbital spacing of planets have implications for how most planetary systems form. In classic planet formation theory, planets form in the protoplanetary disk that surrounds a newly formed star. The planets might form in compact configurations with similar sizes and a regular orbital spacing, in a manner similar to the newly observed pattern in exoplanetary systems.

However, in our solar system, the inner planets have surprisingly large spacing and diverse sizes. Abundant evidence in the solar system suggests that Jupiter and Saturn disrupted our system’s early structure, resulting in the four widely-spaced terrestrial planets we have today. That planets in most systems are still similarly sized and regularly spaced suggests that perhaps they have been mostly undisturbed since their formation.

Continued here.

  1. oldbrew says:

    Iron-rich stars keep planets close to home

    US conference hears star iron content predicts orbital size for exoplanets.

    ‘…stars containing higher levels of iron are more likely to have planets with orbital periods of 8.5 days or less.
    . . .
    …something about forming in a proto-planetary disk that contains relatively large amounts of iron appears to create solar systems with a larger likelihood of close-in planets.
    . . .
    “A star with Sun-like iron content will host warm planets, while stars relatively enhanced in iron will host hot planets, very close in.”
    . . .
    If you want to find planets that aren’t vastly too hot for life, … “your best bet is to look around a star with iron content similar to the Sun”.’

    ‘something about … relatively large amounts of iron’ – Magnetism perhaps?

  2. Geoff Sharp says:

    From my observations our solar system is quite unique. Especially the formation of the 4 outer gas giants. As they are likely to be the drivers of solar grand minima one has to wonder how many star systems are similar in the Milky Way

  3. p.g.sharrow says:

    Geoff says:”our solar system is quite unique” My observation as well.
    Most of what we know about solar system formation is wrong because of that fact!
    The Asteroid Belts are the clue as to the cause…pg

  4. oldbrew says:

    Extra-terrestrial Hypatia stone rattles solar system status quo
    January 9, 2018

    Micro-mineral analyses of the pebble by the original research team at the University of Johannesburg have now provided unsettling answers that spiral away from conventional views of the material our solar system was formed from.
    . . .
    The little pebble from the Libyan Desert Glass strewn field in south-west Egypt presents a tantalizing piece for an extraterrestrial puzzle that is getting ever more complex.

    Read more at:

    In the video a researcher says the stone destroyed an industrial diamond polisher in about 10 minutes.
    – – –
    Libyan Desert Glass

  5. E.M.Smith says:

    Our present system of planet “discovery” is highly biased toward large planets moving fast. To attempt conclusions based on population statistics with a known skewed pool is folly.

    We simply can’t see the transit of anything like a Saturn as it takes more years than we have been observing, nor can we see a Mars as the impact on brightness is too small. Give it another 100 years and we will begin to have an idea what real planetary systems look like.

  6. oldbrew says:

    What we can say is that there are a lot of planetary systems out there with a range of planet sizes, many very close to their star. Some have orbits of only a few days or even less.

    In our solar system nothing is close to the Sun, unless Mercury at ~88 days per orbit is counted.

  7. oldbrew says:

    No planets needed: NASA study shows disk patterns can self-generate
    January 11, 2018

    Astronomers thought patterns spotted in disks around young stars could be planetary signposts. But is there another explanation? A new simulation performed on NASA’s Discover supercomputing cluster shows how the dust and gas in the disk could form those patterns — no planets needed.

    Read more at:

    So more fake exoplanet discoveries than we thought?

  8. oldbrew says:

    ‘This model makes a major prediction that will soon be tested: Extrasolar planets should arise in twin pairs also, with 2-to-1 orbital period resonances common.’ – Tom van Flandern, ‘The Exploded Planet Hypothesis’ [2000]

    Looking good 🙂
    – – –
    The solar system should have had six pairs in TvF’s theory, but due to explosions (see asteroid belt for example) it turned out as we see today (3 pairs with similar rotation periods, and 3:2 length of day in the Venus-Mercury case).
    – – –
    Star Eta Corvi : ‘Two debris disks have been detected orbiting this star, one at ~150 AU, and a warmer one within a few astronomical units (AU)’