Interstellar crashes could throw out habitable planets

August 18, 2011
Interstellar crashes could throw out habitable planets
One of the protoplanetary disks in the Orion Nebula. Credit: NASA / ESA and L. Ricci (ESO)

( -- Our solar system, where planets have a range of sizes and move in near-circular paths, may be rather unusual, according to a German-British team led by Professor Pavel Kroupa of the University of Bonn. The astronomers, who publish their model in the journal Monthly Notices of the Royal Astronomical Society, find that forming planetary systems may be knocked around by crashes with nearby clumps of material, leading to systems where planets have highly inclined orbits and where the smaller (and potentially habitable) worlds are thrown out completely.

The planets in our Solar System, including the Earth, in the same direction around the Sun as the Sun spins, mostly move in paths not so different from circles and are also more or less lined up into a plane not tilted very far with respect to the solar equator. But planetary systems around other stars can be very different, with some worlds moving in the opposite direction to the spin of their stars and with highly tilted orbits. For the first time the team of think they have a convincing explanation for these radically different systems.

Both the shape of and direction of travel of planets in our Solar System were thought to result entirely from the formation of the Sun and planets more than 4600 million years ago. Our local planetary system is believed to have formed as a cloud of gas and dust (a ) that collapsed into a rotating disk under the influence of gravity. The planets then grew from clumps of material within this so-called protoplanetary disk.

The new work suggests that oddly shaped orbits may result from a rather less smooth process. The team think that if the protoplanetary disk enters another cloud of material, it can draw off up to about 30 times the mass of Jupiter from the cloud. Adding this extra gas and dust tilts the disk and hence the angle of the final orbits. Most planetary systems are thought to form in clusters of stars, where the member stars are fairly close together, so these encounters may be very common.

Team member Dr. Ingo Thies, also of the University of Bonn, has carried out computer simulations to test the new idea. He finds that as well as tilting over, loading the protoplanetary disk with material can even reverse its spin, so that it turns in a 'retrograde' sense, where it rotates in the opposite sense to its parent star. At the same time, the encounter compresses the inner region of the disk, possibly speeding up the planetary formation process.

In those circumstances, the simulation suggests that any planets that form will then be in highly inclined or even retrograde orbits. In some cases the orbits may even be tilted with respect to each other, leading to a highly unstable system. One by one, the least massive planets will be ejected completely, leaving behind a small number of 'hot Jupiters', massive worlds that move in orbits extremely close to their star.

In less extreme cases, the disk may only collect a small amount of additional gas and dust and change its tilt by a small amount. This may be what happened in our own Solar System, where the weighted average tilt of planetary orbits to the Sun's equator is about 7 degrees.

Dr. Thies believes the Sun and planets are amongst the more orderly systems. "Like most stars, the Sun formed in a cluster, so probably did encounter another cloud of gas and dust soon after it formed. Fortunately for us, this was a gentle collision, so the effect on the disk that eventually became the planets was relatively benign. If things had been different, an unstable may have formed around the Sun, the Earth might have been ejected from the Solar System and none of us would be here to talk about it."

Professor Kroupa sees the model as a big step forward. "We may be on the cusp of solving the mystery of why some planetary systems are tilted so much and lack places where life could thrive. The model helps to explain why our looks the way it does, with the Earth in a stable orbit and larger further out. Our work should help other scientists refine their search for life elsewhere in the Universe."

Explore further: Astronomers discover 'tilted planets'

More information: The new work is published in "A natural formation scenario for misaligned and short-period, eccentric extrasolar planets", Thies I., Kroupa P., Goodwin S., Stamatellos D. and Whitworth A., Monthly Notices of the Royal Astronomical Society, in press. A preprint of the paper can be seen at

A collection of 30 Hubble Space Telescope images of protoplanetary disks in the Orion nebula is available at
A set of 23 images illustrating the new concept are available from the subfolders at

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1 / 5 (5) Aug 19, 2011
Our solar system . . . may be rather unusual

The most abundant elements in the Sun, in ordinary meteorites, and in rocky planets near the Sun are Fe, O, Ni, Si, S, Mg and Ca [1].

The Sun's iron-rich mantle encases the neutron star at its core. This material is hidden from view by the glowing sphere of waste products - 91 % H and 9% He - that emits photons and is called the photosphere [2].

The outer planets are rich in light-weight elements - H, He, C and N - ejected from the outer stellar layers when the Sun exploded five billion years (5 Gyr) ago to form the solar system [3].

1. "Solar abundances of the elements", Meteoritics 18, 209-222 (1983)

2. "Neutron Repulsion", The APEIRON Journal, in press, 19 pages (2011)

3. "Strange xenon, extinct super-heavy elements, and the solar neutrino puzzle", Science 195, 208-209 (1977)

Oliver K. Manuel
Aug 20, 2011
This comment has been removed by a moderator.
5 / 5 (3) Aug 20, 2011
The most abundant elements in the Sun, in ordinary meteorites, and in rocky planets near the Sun are Fe, O, Ni, Si, S, Mg and Ca [1].
The most abundant are hydrogen and helium and there is no evidence to support Oliver on this. His thinking is not evidence based it is based on his need for it to true because he thinks the Sun has a neutron star in it and an iron mantle despite the total lack of supporting evidence. The lighter elements aren't in the inner solar system because there isn't enough mass to retain it.

This material is hidden from view by the glowing sphere of waste products - 91 % H and 9% He - that emits photons and is called the photosphere [2].
Hidden yet magically Oliver knows it is there. Without evidence of any kind.

The outer planets are rich in light-weight elements - H, He, C and N
Mostly hydrogen and helium just as the rest of the Universe.>>
5 / 5 (3) Aug 20, 2011
- ejected from the outer stellar layers when the Sun exploded five billion years
Utter rubbish based on a none existent event. Those elements are there because that is the norm for the Universe.

Where is the evidence Oliver. It isn't your papers.


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