Friday, March 05, 2010

Hellagrams are great for terrestrial planets

There is an internet petition afoot to make "hella" the official SI prefix for 1027. In one sense, this seems silly- a hellameter is several times the size of the observable universe. But there is at least one application for which this suffix would be useful.

Currently, one of the most exciting areas in all of science is the discovery of smallish planets orbiting other stars. By smallish, I mean smaller than Neptune. But while there is a factor-of-fourteen mass gap in our own solar system between Uranus and Earth, in the rest of the galaxy this gap does not exist, and planets occupy most of that mass range.

Traditionally, most planets have had their mass compared to Jupiter. While this is fine for gas giants, there are a couple of problems when applying it to smaller planets. Firstly, you end up with lots of zeros in front of your number: 0.003 is a bit awkward. Secondly, nobody really has a good feel for how massive a planet is.

The hellagram solves both of these problems. Earth is a shade under 6 hellagrams. Neptune is a shade over 100. Jupiter, the big boy of our solar system, is about 1900. If we assume that Mars is just a bit too small to maintain active geologic processes up to the present day, then 1 hellagram becomes a good ballpark lower bound for active planets. It is also close to the detection limit for Kepler, the most sensitive planet hunting program now operating.

The hella- project is being run out of one of the University of California campuses. And the UC system is a world leader in exoplanetary detection and characterization. So if they get on board the hellabandwagon, the hellagram has a good shot at entering common scientific usage. And that would be hella cool.

The mass of known sub-Neptune planets, in various units:

PSR 1257+12b0.1330.020.00007
GI 581 e11.61.940.00610
PSR 1257+12d22.83.820.0120
PSR 1257+12c24.74.140.0130
61 Vir b30.45.090.0160
Gi 581 c32.05.360.0169
GJ 1214b34.05.690.0179
GJ 667C b34.45.760.0181
GJ 433 b36.16.040.0190
Giliese 876 d38.06.360.0200
HD 40307 c41.06.870.0216
Gl 581 d42.47.100.0223
HD 181443 b45.27.570.0238
HD 1461 b45.47.600.0239
55 Cnc e45.67.630.0240
CoRoT-7 c50.18.400.0264
HD 285968 b50.38.430.0265
HD 40307 d54.79.160.0288
HD 7924 b55.19.220.0290
HD 69830 b62.710.50.0330
HD 160691 c63.110.60.0332
GJ 674 b70.311.80.0370
HD 69830 c72.212.10.0380
OGLE-05-169L b76.012.70.0400
HD 4308 b76.912.90.0405
BD-082823 b85.514.30.0450
HD 125595 b85.514.30.0450
Gl 581 b93.415.70.0492


Chris Phoenix said...

Also, a mole is 6.023 x 10^23, so hella would be a good prefix for talking about the number of atoms or atomic mass units (AMU or Dalton) in macroscopic objects. A kilogram is a bit more than half a hella of AMU's.

As nanotechnology advances, we're gaining the ability to make kilograms of atomically precise nanostructures...


CM said...

I'm convinced. I signed on.