Questions About Planets

I understand that astronomers believe so-called rogue planets were likely ejected from their solar systems early in their planetary histories, but it’s never clear what event(s) could trigger such a thing. My question: What kind of a catastrophic event in our solar system could cause the Earth to become a rogue planet today? It’s ok to be speculative. I’d love to know. Thank you.

Planetary systems become unstable when the orbits of two planets cross.  By this I don’t mean that the planets collide, rather, that their crossing orbits cause them to have a close gravitational encounter.  The close gravitational encounter can transfer a tremendous amount of orbital energy from one planet to the other, potentially shooting it out of the planetary system.

Surprisingly, our own system is barely stable!  A close encounter between the asteroids Vesta and Ceres in about 60 million years ago makes it very difficult to trace Solar system dynamics before the encounter ( and also limits our ability to forward-predict Solar System dynamics on timescales longer than about 10 million years.  For more information about the stability of the Solar system, see this Wikipedia article and its sources:

In summary, to make the Earth a “rogue planet,” the Solar system would have to evolve such that another large body (a large asteroid, or Venus or Mars, or eventually Jupiter) crossed orbits with the Earth.  The asteroids and Mars probably don’t have enough energy to eject Earth.  A more massive planet like Jupiter would be more effective at ejecting Earth, but Jupiter is quite far away and is less likely to cross orbits with Earth.  But the Solar system is definitely stable for the durations of our lives, and this kind of ejection couldn’t happen for at least a few tens of millions of years, if not billions.

Thank you for your inquiry!

Between Dec 2011 and Jun 2012 I observed with the unaided eye a bright light in the western sky from the North American continent, far too bright to be a planetary body, that did not appear to move against the fixed stellar background (between Aquila and Ophiuchus?) and grew brighter as the months passed. As that group of stars made their seasonal procession into the day side of our sky, I lost sight of it.

Hi Astronomy Enthusiast,

You were seeing Venus!  Venus was up in the evening Western sky in the first part of 2012 before its transit in early June (you lost sight of it as it moved farther west and got lost in the brightness of the sun before its June transit).  Of all the planets, Venus appears the brightest because it is close to Earth and very reflective.  (Venus reflects 90% of the sunlight that hits it!)

At its Westernmost excursion, Venus does not appear to move very much relative to the background stars because its motion is mostly along our line of sight, rather than across it.  Venus appears to move most near the sun (such as during a transit) when its motion is across our line of sight.


Is there any work being done to try to identify such planets around either Alpha Centauri A or B? Is there somewhere I can go to on the web to see what the current thinking and evidence is from any work on these stars and their surrounding planets, and whether any might be in the ‘goldilocks’ zone for these stars?

There is a paper reporting the detection of an Earth-mass planet around Alpha Centauri B.  See Phil Plait’s blog for a great synopsis of the paper.

Alpha Centauri, as you can imagine being the nearest star system to our own Sun, has been extensively studied for many years to determine whether it has planets.  Last year a roughly Earth-mass planet was reported around Alpha Cen. B orbiting at 0.04AU (about a tenth of the orbital distance of Mercury), however there is considerable controversy surrounding this discovery and it has yet to be confirmed.  The existence of any planets larger than around Neptune has already been ruled out in the Alpha Centauri system, however finding, or ruling out, small, Earth-size, planets at Earth-like orbital distances is exceptionally difficult.  The Wikipedia article on Alpha Centauri Bb actually does a very good job of summarising the current situation.

How long it will take mankind to identify a habitable planet that would become the candidate for our first planetary colony? Do you think this is going to happen in the next, say 5-10 years with the TESS and E-ELT coming on line? Or, if it might take longer, how long?

Anything regarding colonisation of other worlds is of course highly speculative.  However I’m not above a little speculation so here are my thoughts.

Firstly I would say that the first permanent human settlement on another world would almost certainly be in our own solar system, so in that sense we already know of the planet or moon in question. Which solar system body would host that first colony is another round of speculation, the Moon or Mars are the most frequently touted, though I’ve always been rather fond of the idea of cloud cities on Venus.

In terms of identifying the planet that might eventually become the first extrasolar human outpost, I strongly suspect it would be more than 10 years away.  TESS is due for launch in 2017, but the E-ELT is not expected to be completed until 2022 and the James Webb Space Telescope is not expected to launch until late 2018/early 2019.  So already just in terms of getting these facilities ready we’re looking a fair distance into the future.  One then needs to consider whether any of these facilities are going to find a potential ‘Earth 2.0’ and if so how long that would take.

TESS will not find direct Earth analogs, the planets it finds will have orbital periods of no more than 2 months, so finding planets in the habitable zone of a sun-like star is not something it can do. It should however find Earth-size planets in the habitable zones of dimmer, less massive stars.  Where the Kepler mission went for finding smaller numbers of longer period planets, TESS is intended to find vast numbers of shorter period planets.  TESS by itself would also not be able to tell us whether any of these planets would be nice places to live, it can provide us with a sample of Earth-sized planets in the habitable zones of cool stars, however we will then need to study those planets further.  That will be where JWST and the E-ELT, as well as some new instruments on existing telescopes, come in, trying to study the atmospheres of these planets to give us a better idea of what they are like.  Studying the atmospheres of extrasolar planets is very difficult however, at the moment we have really only managed to get good atmospheric properties for a small number of hot-Jupiter type planets (massive planets very close to their host stars).  The new telescopes and instruments coming online in the next decade will certainly allow us to significantly improve on what we have now, but getting at the atmospheres of truly Earth-like, mostly rocky, planets will still be far from easy, and certainly I don’t think we’ll be able to tell whether humans would be able to live there.

We might get lucky and it may turn out that one of the planets that we discover in the next decade does turn out to be our ideal second home, though I think that is far from certain, and I don’t think we’ll be able to tell until at least the generation of facilities beyond those currently planned.  The way these cycles go that future generation of facilities won’t be here for 20-30 years.

That may sound a bit pessimistic, but we are edging closer every day, and compared even with the time since the invention of the telescope, 30 years is just round the corner!

I wonder if there is anyone on your staff, or anyone you can refer me to get the facts on the story about a rogue planet that has an orbit perpendicular to the elliptical plain of the other planets and which is Gmail Planet
X and the year 2012 supposed to hit the Earth in 2012? As a former Astronomy student I know it’s a bunch of junk, but I’d like to get some more detail if possible. The issue I’m dealing with is my town has an end of the world cult preparing for the collision and we would like to get the real story out.

I have heard similar ideas about the Earth/Solar System/Universe ending in 2012 (due to the Mayan calendar running out and a variety of other such nonsense). After scouring the literature and doing some digging on the web it seems that Wikipedia actually has a pretty concise and very accurate and welldocumented version of the whole story behind the Undiscovered Planet and the destruction of Earth (or lack thereof). I recommend reading these two pages on Wikipedia: Planets Beyond Nepture and Zeta Talk

The first one is very scientific and presents both sides of the argument, as well as the final conclusion of astronomers today (“Today the overwhelming consensus among astronomers is that Planet X, as Lowell defined it, does not exist” i.e. there is no extra planet that we don’t know about or that is being kept secret from most humans and thus nothing will crash into Earth and destroy life in 2012). The second one is more about some of the history of these wild claims.