Last Thursday, I came across a casual conversation in my facebook “news” feed. I’ll call the two participants A and B.
It all started with A posting a link about a rather large number of people “fleeing Rome” last Wednesday because, back in 1915, some seismologist had apparently made a prediction about a catastrophic earthquake happening on that date. Everything else followed from there.
B: They might wonder if it’s a coincidence that the earthquake happened in Spain instead.
A: yes indeed!
B: This is probably dumb because I don’t know enough of the science to comment, but if the position of a distant planet can perturb the orbit of a gas giant orbiting close to its star, to the point that it rotates in the opposite direction, then why couldn’t certain alignments generate forces that might affect plate movements? Is it that such calculations can’t be that specific because of other variables?
A: You have to compare the force of gravity (F=ma) in the two situations to know the answer.
I guess for the first situation, you’re thinking about this? I would need to look at the research paper to get their simulation details, but the reason is still gravity.
For the second situation, add up the gravitational forces and see how little effect on Earth that is. Remember the gas giants are pretty far from the Earth, and there is that r^2 in the denominator.
Roughly one day later:
A: This hot jupiters orbiting retrograde topic was one of those discussed at our Friday morning science meeting… it’s far more interesting than I first thought. Yes, it’s a gravitational effect, but it’s a subtle one arising from …the gravitational forces for the several interacting bodies. If you expand the interacting forces, there is a primary r(distance between the bodies)^2 term plus a less strong r^4 term and a less strong r^8 term and less strong higher order terms. The r^8 term which they call the octopole term (I hope I’m understanding correctly) over time adds up so that every once in a while it cases large changes in the eccentricity of a planet’s orbit, which causes the planet to change its orbit and become retrograde. It almost looks to me like it’s a chaotic effect.
Then our morning discussion expanded to discuss hot Jupiters generally and the enormous just released Kepler data set. When hot Jupiters were first found by the radial velocity method 15 years ago, those types of planets were found everywhere, but that was due to the method because they are the easiest to find. Then all of the theoreticians scrambled to try to explain them, and it wasn’t easy, and they still can’t explain every aspect. Now the Kepler data has shown that hot Jupiters are in fact rare, and not only that, our own solar system doesn’t look like the typical ones in the Kepler data either. We should have more terrestrial planets at Mercury’s orbit, and we seem to need another ice giant (Neptune-like) to explain Mercury. If our solar system lost the ice-giant, it could be anywhere in the galaxy by this time. In fact there should be a lot of ejected free-floating planets around from similar scenarios all over the galaxy.
Summation: Scientists’ planet formation models could be completely wrong based on what is seen in the Kepler data.
B: Thank you, A. That’s juicy stuff. Tonight I skipped ahead to disc 7 in the Filippenko course, which begins with “The Formation of Planetary Systems,” so this is timely information. Astronomy seems to be on fast forward!
There are so many things in this conversation that I absolutely adore – I don’t really know where to start. First, there’s simply the fact that it’s possible to stumble across such a “casual conversation” about serious science on facebook on a weekday morning. I love it. Then there are the explanations A is giving B. Even I can understand them (at least I think so… kind of). There’s the twist where A goes away for a little while, thinking about all of it, and comes across new fodder for the conversation which she then brings back to explain further and expand on the topic. Then there’s the little jolt of surprise to hear that, apparently, planets can go missing. (And that there may be a whole lot of missing planets flying around, apparently. I thought this only happened in Doctor Who.)
And, last but not least, there’s the statement at the end:
Scientists’ planet formation models could be completely wrong based on what is seen in the Kepler data.
Honestly, I have no idea why so many people think scientists are only happy when they’ve figured something out. What gets us really excited is when we realize that what we thought we had figured out turns out to be partially – or completely – wrong. The possibilities!…..
Anyway, another casual conversation this week, which in this case I was involved in, was a chat over dinner with one of the directors of the European Space Agency. As you would, we started asking him about the Gaia satellite.
What will Gaia do? Some highlights from the mission summary:
- Gaia will conduct a census of a thousand million (yes, that’s one billion) stars in our Galaxy, monitoring each of its target stars about 70 times over a five-year period. It will precisely chart their positions, distances, movements, and changes in brightness.
- It will map the motions of stars, which encode their origins and evolution.
- Gaia will provide the detailed physical properties of each star observed, revealing luminosity, temperature, gravity and composition.
- It will repeatedly measure the positions of all objects down to magnitude 20 (about 400 000 times fainter than can be seen with the naked eye). Variable stars, supernovae, other transient celestial events and minor planets will all be detected and catalogued to this faint limit.
- Gaia will measure the position of all objects brighter than magnitude 15 (4000 times fainter than the naked eye limit) to an accuracy of 24 microarcseconds (comparable to measuring the diameter of a human hair at a distance of 1000 km.)
- The distances of the nearest stars will be measured to an accuracy of 0.001%.
And this is what we’ll get from it:
- Gaia’s main goal is to clarify the origin and evolution of our galaxy.
- It will test theories of star formation and evolution.
- It will probe the distribution of dark matter.
- It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and failed stars called brown dwarfs. Within our own Solar System, Gaia should also observe hundreds of thousands of asteroids.
- Amongst other results relevant to fundamental physics, Gaia will follow the bending of starlight by the Sun’s gravitational field, as predicted by Albert Einstein’s General Theory of Relativity, and therefore directly observe the structure of space-time.
Yes, I was also wondering who will process all that data, and where. It will be downloaded from the satellite daily and analysed by an international group of scientists located in different countries, the Gaia Data Processing and Analysis Consortium (DPAC). There will be intermittent releases, but final results are not expected to be published until 2020.
!!!Imagine all the stuff that’s going to come up over the next decade!!!
As B said in that discussion up there: astronomy does seem to be on “fast forward” – so much so that even a down-to-earth biological oceanographer like me could easily find herself starting to get excited about it…