Starship of the Planet Earth

Starship of the Planet Earth

If the Ionian spirit had won, we – a different “we”, of course – might be now be venturing to the stars. Our first survey ships to Alpha Centauri and Barnard’s Star, Sirius and Tau Ceti would have returned long ago. Great fleets of interstellar transports would be under construction in Earth orbit – unmanned survey ships, liners for immigrants, immense trading ships to plow the seas of space. On all these ships there would be symbols and writing. If we looked closely, we might see that the language was Greek. And perhaps the symbol on the bow of one of the first starships would be a dodecahedron, with the inscription Starship Theodours of the Planet Earth.

In the time line of our world, things have gone somewhat more slowly. We are not yet ready for the stars. But perhaps in another century or two, when the solar system is all explored, we will also have put our planet in order. We will have the will and the resources and the technical knowledge to go to the stars. We will have examined from great distances the diversity of other planetary systems, some very much like our own and some extremely different. We will know which stars to visit. Our machines and our descendants will then skim the light years, the children of Thales and Aristarchus, Leonardo and Einstein.

We are not yet certain how many planetary systems there are, but here seem to be a great abundance. In our immediate vicinity, there is not just one, but in a sense four: Jupiter, Saturn and Uranus each has a satellite system that, in the relative sizes and spacings of the moons, resembles closely the planets about the Sun. Extrapolation of the statistics of double stars which are greatly disparate in mass suggests that almost all single stars like the Sun should have planetary companions.

Galaxy is cultivated. Very soon we’ll definite answers to which of the hundred nearest stars have large planetary companions. (Quotations from Megan Jorgensen). Image: © Megan Jorgensen (Elena)

We cannot yet directly see the planets of other stars, tiny points of light swamped in the brilliance of their local suns. But we are becoming able to detect the gravitational influence of an unseen planet on an observed star. Imagine such a star with a large “proper motion”, moving over decades against the backdrop of more distant constellations; and with a large planet, the mass of Jupiter, say, whose orbital plane is by chance aligned at right angles to our line of sight.

When the dark planet is, from our perspective, to the right of the star, the star will be pulled a little to the right, and conversely when the planet is to the left. Consequently, the path of the star will be altered, or perturbed, from a straight line to a wavy one. The nearest star for which this gravitational perturbation method can be applied is Barnard’s Star, the nearest single star. The complex interactions of the three stars in the Alpha Centauri system would make the search for a low-mass companion there very difficult.

Even for Barnard’s Star, the investigation must be painstaking, a search for microscopic displacements of position on photographic plates exposed at the telescope over a period of decades. Two such quests have been performed for planets around Barnard’s Star, and both have been by some criteria successful, implying the presence or two or three planets of Jovian mass moving inn an orbit, calculated by Kepler’s third law, somewhat closer to their star than Jupiter and Saturn are to the Sun. But unfortunately, the two sets of observations seem mutually incompatible. A planetary system around Barnard’s Star may well have been discovered, but an unambiguous demonstration awaits further study.