Astronomy Now Home
Home Magazine Sky Chart Resources Store

On Sale Now!



The August 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








"Ping-pong" planets bounce between stars
DR EMILY BALDWIN
ASTRONOMY NOW
Posted: 07 February 2012


Bookmark and Share

A gravitational ping-pong match lasting up to one million years could be in play between nearby binary stars, say Cambridge University scientists.

It is widely accepted that planets can be ejected completely from a solar system, especially during the dynamically chaotic period early in the solar system's life where planets are jostling for the most stable orbits (see Jumping Jupiter ejected giant planet and Free-floating planets more common than stars?). Recently, exoplanets have been found in two and even three-star systems, and in the new study, Nickolas Moeckel and Dimitri Veras of the Institute of Astronomy, Cambridge, show that a planet ejected from orbit around one star could find itself passed onto its binary companion. Furthermore, the planet may get "bounced" between the stars, providing one possible explanation for the eccentric orbits of some exoplanets.


Planets could be kicked out of one star's clutches only to be sent careening around – or even into – its binary companion. Image: NASA, ESA, and G. Bacon (STScI).

Moeckel explains that there are two key elements required for this phenomenon. "First, the stars need to be on a wide enough orbit so that one is not interfering with planet formation around the other," he says, stressing that this is distinctly different to the recently announced 'Tatooine'-like planets, where the planets are in orbit around both stars of a closely separated binary (see Planets discovered with double Sun-like stars). "Second, there need to be multiple planets around one of the stars. The orbital instability that leads to the bouncing phenomenon requires that two planets come in close proximity to each other – this happens more easily and faster with multiple closely spaced planets."

In the new computer models, the bouncing effect typically occurs for stars separated by between six and 25 times the distance between the Sun and Pluto. Up to 85 percent of the ejected planets will make at least one journey through the companion star's space, and between 45 and 75 percent will bounce repeatedly, depending on the initial orbital parameters of both systems.

"Rarely a planet that begins bouncing will settle back into its original planetary system, but this is done at the expense of one of the other remaining planets, which will itself be ejected or collide with a planet or star," says Moeckel. "Once the bouncing begins, typically the planet will eventually end up leaving the binary system."

This planetary ping-pong game lasts for up to one million years and could result in the stars swapping their planets. With such wildly erratic orbits, habitability of these planets is out of the question, with searing hot temperatures as the it swings around the host star, and freezing cold temperatures as it is flung back out into space.

As for examples of this happening in the ever-growing exoplanet database, "we don't yet have enough observational constraints on the number of systems in nature that match our simulations to give a good estimate," says Moeckel. "We could see a planet in the process of bouncing if we were able to measure all parts of the binary system precisely, particularly if we notice the planet residing 'in-between' the two stars."

The paper has been accepted for publication in MNRAS and was posted online on arXiv on 31 January.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.