Planets around other stars are like peas in a pod

January 9, 2018, University of Montreal
The Kepler-11 planetary system is one of the multi-planet systems studied by Dr. Weiss and her colleagues. Credit: NASA/T. PYLE

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. 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 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 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 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.

To test that hypothesis, Weiss is conducting a new study at the Keck Observatory to search for Jupiter analogs around Kepler's multi-planet systems. The planetary systems studied by Weiss and her team have multiple planets quite close to their star. Because of the limited duration of the Kepler Mission, little is known about what kind of planets, if any, exist at larger orbital distances around these systems. They hope to test how the presence or absence of Jupiter-like planets at large orbital distances relate to patterns in the inner planetary systems.

Regardless of their outer populations, the similarity of planets in the inner regions of extrasolar systems requires an explanation. If the deciding factor for planet sizes can be identified, it might help determine which are likely to have terrestrial that are suitable for life.

The article "The California-Kepler Survey V. Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced" is published in The Astronomical Journal.

Explore further: Discovery of new planet reveals distant solar system to rival our own

More information: Lauren M. Weiss et al. The California-Kepler Survey. V. Peas in a Pod: Planets in a Kepler Multi-planet System Are Similar in Size and Regularly Spaced, The Astronomical Journal (2018). DOI: 10.3847/1538-3881/aa9ff6 , iopscience.iop.org/article/10. … 538-3881/aa9ff6/meta

Related Stories

The latest Kepler Orrery video

November 7, 2013

If you've ever wanted to know what 3,538 exoplanets look like spinning around their stars, here you go!

Is our solar system weird?

July 18, 2014

Is our Solar System normal? Or is it weird? How does the Solar System fit within the strange star systems we've discovered in the Milky Way so far?

Recommended for you

Unconfirmed near-Earth objects

June 22, 2018

Near-Earth objects (NEOs) are small solar system bodies whose orbits sometimes bring them close to the Earth, potentially threatening a collision. NEOs are tracers of the composition, dynamics and environmental conditions ...

HESS J1943+213 is an extreme blazar, study finds

June 21, 2018

An international group of astronomers have carried out multi-wavelength observations of HESS J1943+213 and found evidence supporting the hypothesis that this gamma-ray source is an extreme blazar. The finding is reported ...

'Red nuggets' are galactic gold for astronomers

June 21, 2018

About a decade ago, astronomers discovered a population of small, but massive galaxies called "red nuggets." A new study using NASA's Chandra X-ray Observatory indicates that black holes have squelched star formation in these ...

The Rosetta stone of active galactic nuclei deciphered

June 21, 2018

A galaxy with at least one active supermassive black hole – named OJ 287 – has caused many irritations and questions in the past. The emitted radiation of this object spans a wide range – from the radio up to the highest ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Knecht
4 / 5 (2) Jan 09, 2018
Hmmm, like the spacing of atomic orbitals in highly excited Rydberg atoms?

rrwillsj
1 / 5 (1) Jan 10, 2018
K, do you think it might be causation by a similar phenomena? On a different scale of course. What experiment(s) do you intend to prove or disprove that speculation?
mackita
not rated yet Jan 10, 2018
@rrwillsj: The atomic orbitals in highly excited Rydberg atoms are called Kepler orbits traditionally. There are already theories which link the Titius-Bode law to gravitational waves resonance. I presume, they're rather dark matter waves, nevertheless the similarity with quantum wave forming orbital remains apparent there.
milnik
not rated yet Feb 24, 2018
Planets like all celestial bodies move according to natural laws, and this takes place throughout the universe. The basis for the movement is: the sum of the kinetic and potential energy of the two bodies, rotating one against the other, is a constant. The second condition is: the kinetic energy of the radial velocity of the celestial body, transformed at the moment of the coupling of two spins of the same size, and the opposite directions. One spin is its own, and the other is a rotation of a smaller body by a sinusoidal radius around the center of the mass (pericenter). When it comes to science, it will come to know the true paths of heavenly bodies, going from the planet's satellites to the galaxy clusters. Tell them to seek help.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.