Five radial velocity datasets (published last year by Marcy et al. 2005) have just been added to the systemic console: HD 183263, HD 117207, HD 188015, HD 45350, and HD 99492. Each of these more-or-less sunlike stars is too faint to be seen with the naked eye, and each is accompanied by (at least) one detectable planet. The periods range from 17 days to several years. None of these planets were extraordinary enough to warrant much fanfare in the popular press. (Ten years ago, however, the announcement of 5 planets would have been front page news. Ahh, those were the days!)
When you use the console to obtain orbital fits to these systems, you’ll notice that several of the stars have a long-term radial velocity trend superimposed on the variations that arise from the much more readily detectable shorter-period planet. These velocity trends are likely caused by as-yet undetected massive planets lying further out in the systems, and as these stars are monitored over the long term, the orbits of these distant, frigid giants will gradually reveal themselves.
In the meantime, the residual velocity trends underscore an interesting general property of extrasolar planets. The presence of a known planet is the best indicator that a given star harbors detectable (but as-yet undetected) planetary companions. That is, if you want to find new planets, then look at stars that already have known planets. Indeed, six of the first twelve planet-bearing stars that were monitored for more than two years at Lick Observatory were subsequently been found to harbor additional bodies. This impressive planetary six-pack includes luminaries such as Upsilon Andromedae, 55 Cancri, and 47 UMa, in addition to the more pedestrian Tau Boo, HD 217107, and HD 38529. (See Fischer et al. 2001).
Frequent visitors to oklo.org will have noticed a definite fall-off in the number of recent posts. This was a direct result of the start of the winter quarter here at UCSC, but now things are rolling, and the systemic team is working hard to prepare the next phase of the collaboration.
Last week was also the 207th meeting of the American Astronomical Association. I took a one-day trip to Washington in order to give a talk at Tuesday’s extrasolar planets session entitled, “From Hot Jupiters to Hot Earths“. I teach class on both Monday and Wednesday mornings, so the trip was more of a lightning raid.
I arrived at Dulles Airport at 6 am, after an overnight flight. My talk wasn’t finished, so I sat in an empty departure lounge for several hours and worked on the slides. By mid-morning, I realized that I had better head to the venue. I took a cab to the conference hotel, tapping on the laptop for most of the way.
Let a pebble slip from your hand and it falls straight to the ground. Toss the pebble sideways, and it traces a parabolic arc through the air. Imagine throwing the pebble sideways with even more speed. It lands further away. Imagine throwing the pebble with such great velocity that the surface of the Earth begins to curve away beneath it as it falls. In the absence of air friction, a pebble thrown sideways with sufficient velocity will fall in such a way that the Earth curves continuously out from underneath. The pebble falls endlessly without ever touching the ground. It is in orbit.
The idea that an orbit is the state of a body in continual free-fall can be traced to the 1600s, and was first stated in print by Robert Hooke, whose paper entitled, “The Inflection of a Direct Motion into a Curve by a Supervening Attractive Principle” was read to the Royal Society on May 23rd 1666. Robert Hooke’s fame and reputation have spent the last three hundred and twenty years in Newton’s shadow, but he was a tremendously inventive scientist, and indeed, was one of the founders of what we now consider the scientific method. (See, for example, the recent Hooke biography, “The Forgotten Genius” by Stephen Inwood). Hooke, drawing on the earlier ideas of William Gilbert and Jeremiah Horrocks, and profiting from conversations with fellow Royal Society member Christopher Wren, realized that if the Sun exerts an attractive force on bodies in space, then “all the phenomena of the planets seem possible to be explained by the common principle of mechanic motions.” Hooke had an intuitive (but non-mathematical) understanding of the the orbit in the sense described in the paragraph that opens this post.
On Dec. 12, 2005, we arrived at Kansai with the Sun low on the horizon, casting orange shafts through the plane. Whitecaps were frothing on the Inland Sea. The airport is built on two 4 kilometer by 1 kilometer artificial islands, and is connected to Honshu by a 3 kilometer bridge that cost 100 billion yen. Beneath the vast new terminal, an attendant with a pressed shirt and tie helped us navigate the ticket machines to buy two Haruka Ltd. express tickets to Kyoto. The bullet train pulled away as soon as we stepped on, gliding glass-smooth through the night blur of an endless city.
That night, in a room in the hyper-modern Hotel Granvia, I lay awake, jet lagged and alert, listening to the faint rush of warm air flowing from a network of unseen ducts. Outside, the lights of the city were a panoply of mysterious characters and sparkling complexity, illuminating blocks of buildings that stretched away in all directions to the dark mountainous horizon. I was suddenly brought around to a simple fact that I always find startling:
No one arrived from outer space to build all this. In a very real sense, the planet Earth has done has done all this itself.