Gravitational Anomalies in the Solar System

I found this article at the physics arXiv blog (which incidentally is a fascinating site in itself), entitled The Puzzle of Astronomy's Unexplained Anomalies, pointing to the actual arXiv paper Astrometric Solar-System Anomalies. I had heard of several of these, but there were a few new ones to me as well. The five anomalies mentioned are:

1) The Fly-by Anomaly -- very well-established but completely unexplained.

2) The slow but steady increase in the length of the Earth-Sun distance (with no change in the length of the sidereal year), about 15cm per year. This is also fairly well-established (it had been found by Earth-Mars ranging data using the recent Martian spacecraft) but defies explanation. In conventional physics this would only be possible if the Sun were steadily gaining mass, whereas it appears to be steadily losing mass, so that Earth's orbit (with no change in the length of the sidereal year) should be SHRINKING.

3) The Pioneer Anomaly -- the most well-known effect, and still not convincingly explained.

4) The steady unmodeled increase in the Moon's eccentricity, measured by the Apollo laser ranging experiments as about 9 x 10^-12/yr. This is on top of all modeled changes due to conventional physics, such as the expected change due to tidal effects (7 x 10^-12/yr).

5) The Saturn orbit anomaly -- found by tracking the Cassini spacecraft, this is an unexpected, unexplained, precession of Saturn's perihelion.

Any one of these might have a conventional explanation, but taken together, they look to me like convincing evidence that new gravitational physics is required. You could also add the two longer-range anomalies:

6) The galactic rotation curve / visible galactic mass discrepencies. The most accepted explanation for this is so-called "dark matter", but I am thoroughly unconvinced of its existence. MOND describes the effect almost perfectly, but sadly lacks theoretical underpinning.

7) The accelerating universal expansion rate, discovered by looking at distant supernovae. Again, the most accepted explanation for this is so-called "dark energy", but I am dubious.

I personally suspect that all of these are side-effects of the same underlying cause. What that cause might be, I do not know. But I do know that the currently accepted theory of gravity, since it fails to address that cause, must be incorrect. (The fact that it has also proven impossible to quantize is a big hint in that direction too).

Bill

How can tracking Cassini be used to detect perihelion changes in Saturn's orbit if Cassini has been at saturn for less than a Saturnian year? (indeed, less than half of one)

From the abstract of the arXiv paper:

The astronomer E.V. Pitjeva, by analyzing with the EPM2008 ephemerides a large number of planetary observations including also two years (2004-2006) of normal points from the Cassini spacecraft, phenomenologically estimated a statistically significant non-zero correction to the usual Newtonian/Einsteinian secular precession of the longitude of the perihelion of Saturn, i.e. \Delta\dot\varpi_Sat = -0.006 +/- 0.002 arcsec/cy; the formal, statistical error is 0.0007 arcsec/cy.

So it sounds like earlier observations were included in the analysis of Saturn's orbit, where the Cassini-related observations were doubtless the most accurate, but the overall timescale was long enough to establish the effect.

Bill