“Planet X” lost in space?

29 09 2010

Where is Planet X? It may have escaped the solar system or may not exist at all, say fossil researchers. (Credit: Ben McGee)

Researchers at the University of Kansas and the Smithsonian Institute have performed one of the most extensive analyses of Earth’s past extinction patterns to date.  So, what did researchers Adrian Melott and Richard Bambach conclude?  Planet X cannot exist.

Planet X, also known as Nemesis, is a proposed “dark” (i.e. dim) companion star to the sun, such as a red dwarf or brown dwarf, that sits at an extreme distance and orbits once every 26-million years or so (see other related Planet X blogs here and here).  Conventional Nemesis theory holds that as Nemesis is knocked around by the gravity of nearby stars in the galactic plane, the dark star perturbs the Solar System’s Oort cloud, a shell of icy fragments surrounding the solar system, and sends a shower of comets into the solar system, causing impacts and ultimately – extinctions.

The problem that Melott and Bambach found is that:

  1. According to galactic gravity fields, Nemesis cannot have an exceedingly stable orbit,
  2. The extinction patterns in the fossil record are too regular to be caused by something orbiting the way Nemesis would.

The Solar System moves up and down through the galactic plane as it orbits the Milky Way, carrying the Earth and other planets, (and Nemesis if it is there) along with it.  Well, this up-and-down motion can be roughly measured and tells us that the Solar System passes through the galaxy’s plane less than twice every 54-million years.  If true, that means a perturbation of the Oort cloud because of Nemesis interacting with the galactic plane once every 27-million years doesn’t line up quite right.

This difference was brought into sharp relief by Melott and Bambach, who measured the regularity of fossil record extinctions with meticulous detail using multiple methods, and they found that the period of extinctions is too sharp.  They suggest looking for alternate mechanisms to explain these surprisingly regular apocalyptic events.

So, is Planet X gone?  Another possibility is that we lost it.

If Nemesis’s orbit were too unstable, being perturbed by nearby stars as the Solar System passes through the galactic plane, (think having someone push you regularly on a swingset,) eventually it achieves an escape trajectory and becomes “unbound” – a rogue star in the galaxy no longer gravitationally-linked to us.

In that case, we’d never know – a free dwarf star in the interstellar medium is extremely difficult for astronomers to find.  (i.e., currently impossible.)

So, in an ironic twist, has the Nemesis theory been destroyed by the extinction record that engendered it?

Only time will tell.


Solar System has more than one “Planet X”?

12 06 2010

Recent observations of the nearby (44 light-years away) multi-planet star system Upsilon Andromedae have kindled in my mind an intriguing question:  Namely, can our own solar system have one or perhaps many “Planet Xs” hiding in oblique orbits?  Allow me to explain.

New findings show Upsilon Andromedae's planets have oblique orbits. Credit: NASA, ESA, A. Field

It has been known for quite some time that the Upsilon Andromedae star system is composed of at least three Jupiter-sized planets (we can’t yet see Earth-sized planets or smaller, yet).  However, research recently presented at the American Astronomical Society suggests that unlike our solar system where the major planets orbit in the same plane, two of Upsilon Andromedae’s three known planets orbit askew with respect to each other to the tune of nearly 30 degrees tilt.  This defies what we have come to know as a “normal” star system configuration of planets.

While there have been many “Planet X” hypotheses in our own star system over the years, including recent research suggesting the possibility of a large, distant icy planet in our own solar system, (see Tyche post here,) astronomers have not yet been able to locate any of these proposed culprits of periodic extinctions or comet peculiarities.

However, planets are notoriously difficult to find, especially the farther away from the Sun they are.  Planets do not intrinsically emit their own light (except infrared), and their reflections get exponentially dimmer with distance.  So, with the recent Upsilon Andromedae findings in mind, perhaps the reason we’ve yet to find any Planet Xs isn’t because there’s no merit to the ideas, but rather that astronomers have been looking in the wrong orbital planes.

Let’s investigate a step further. With “ordinary” planet formation in a young star system, the conservation of angular momentum causes material around a new sun to flatten into a disk, (called a “proplyd” or protoplanetary disk,) and planets form from the material in this disk.  Hence, planets will be found in an orbital plane around a star, just like ours are.  However, when we look closely, we find that there are even notable oddities in our solar system.  Namely, Uranus is tilted almost completely 90-degrees onto its side, and Pluto is not only tilted sideways, but it also orbits obliquely, much like its Jupiter-sized kin in Upsilon Andromedae.  What does this mean?  At the very least, it means that the evolution of any star system is a dynamic process.  At most, this is an indicator that we’ve yet to fully describe our own system.

On this note, Upsilon Andromedae is actually a “quiet” binary star system.  The main star, Upsilon Andromedae A, is a yellow-white star not unfamiliar to human eyes.  However, it does have a dim, red dwarf brother (unsurprisingly called Upsilon Andromedae B) in a wide orbit, far enough away to leave the planets orbiting Upsilon Andromedae A alone, so far as we are able to tell.  However – it does beg the question: Might subtler interactions of Andromedae’s red dwarf or perhaps outer, dimmer planets we have yet to find be responsible for the oblique orbits we see?  And if so, have we found a distant mirror suggesting there might be more places to look for Planet X in the far reaches of our own system?

Food for thought.

Solar System’s “Planet X” Returns!

30 04 2010

Researchers propose new planet "Tyche" on distant fringe of solar system. Inner planets on this diagram are too close to the Sun to see. (Credit: Ben McGee)

Our solar system may have just gotten a lot more interesting. Researchers studying the orbits of comets at the University of Louisiana have found a problem.  -They’ve discovered an inconsistency with how comets are spread out compared to what you would expect under ordinary galactic conditions.  In an article recently submitted to the journal Icarus, they propose the existence of another behemoth planet orbiting far beyond Pluto along the outskirts of the Oort Cloud (a huge sphere of proto-comets  that surrounds the solar system) and that this proposed planet, Tyche, is responsible for what they see.

This calls to mind another similar hypothesis based on the apparently cyclical nature of mass extinctions throughout Earth’s history and on geologic evidence from the Moon.  Called the Nemesis theory, it proposes that our solar system is actually a binary star system, and that the Sun’s twin is a small, dim, red dwarf star named Nemesis orbiting far beyond the Oort cloud.  As the theory goes, Nemesis passes close enough to the Oort cloud to send a deadly rain of comets into the inner solar system every few-score-million years or so.  The name here is completely appropriate, as those familiar with Greek Mythology will recall that Nemesis is the goddess of Retribution.

While the Tyche and Nemesis models are clearly different proposals, the researchers offering the new proposal are aware of the similarities.  According to Greek Mythology, Tyche is Nemesis’s good sister, the goddess of Fortune and Luck.  Say what you will about the penchant of astronomers to lean on mythology – I think it’s clever.

With all of these findings hinting at something going on in the outer solar system, it seems as though there’s something there to find.  A cold gas giant would be fascinating, as would the revelation that our Sun has had a twin all along.

Maybe even both.

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