232601
229719
Skywatching

The world that never was

Neptune was the first planet discovered by detecting and measuring deviations of known planets from the predicted orbits.

From these measurements astronomers calculated how big a body was causing it and where to look.

The sky is a very big place, especially when we are looking through telescopes that can see only a tiny bit at any one time. We need to know where exactly to look, and when.

After this method triumphed in finding Neptune, the search was on for other unknown planets. Almost immediately, the attention of astronomers was drawn to Mercury, the closest planet to the Sun. There was something funny about the planet's orbit.

All the planets have very slightly egg-shaped orbits, so there is one point where they are at their closest to the Sun (the perihelion) and at the other end of the orbit, where they are at their furthest (the aphelion).

Strangely, instead of the orientation staying fixed compared with the stars, it was slowly slipping, or precessing. Something had to be causing it, maybe an unknown planet.

Astronomers made measurements, calculated, and then concluded the perturbations to Mercury's orbit indicated there was a planet orbiting the Sun even closer than Mercury.

They were so sure that even before the planet had been found, it was given a name, Vulcan, after the Roman god of fire. Temperatures on the surface of Mercury are high enough to melt lead. Vulcan would be far hotter.

Mercury is a hard planet to observe. Since it orbits close to the Sun, most of the time it is lost in the Sun's glare. We only get to see it when it is at the eastern or western extremes of its orbit.

Then, it is at a large enough angle from the Sun for it to rise in a reasonably dark sky before sunrise, or to set long enough after the Sun for most of the glare to have gone.

Vulcan was expected to be far harder to find, so even when astronomers searched the predicted positions and failed to find it, they were convinced it was probably there, somewhere, and continued searching.

There was the odd report of someone actually finding it, but the observations could not be repeated and were not consistent. Finally, in the early years of the 20th Century, someone came up with a new branch of physics that offered a completely different explanation for the problems with Mercury's orbit.

The scientist was Albert Einstein and the explanation for the orbit problems was the distortion of space-time due to being close to the large mass of the Sun.

All objects bend space-time, similar to the distortion of a trampoline when we drop a bowling ball or other heavy object on it. Because Mercury's orbit takes it nearer to and further from the Sun, it moves between its perihelion, where space-time is more distorted, out to its aphelion, where it the distortion is less.

It is this that causes the orbit to precess, and Vulcan became the "planet that never was,” or maybe not. What, if anything did those reports of sightings of Vulcan mean?

There are two satellites sharing Earth's orbit around the Sun, one leading and one trailing. The pair, called STEREO is being used to make high quality, 3D images of the Sun and coronal mass ejections, and to provide a more complete view of our star.

A search through the STEREO database has come up with nothing, which means there is nothing there bigger than about six-kilometre diameter, other than asteroids with orbits taking them close to the Sun and then far out into the Solar System.

The only planet Vulcan we know of is the fictional Mr. Spock's home world. That planet is said to orbit the star 40 Eridani A, which lies 16 light years away.

Astronomers recently discovered a planet orbiting that star. Guess what they called it?

  • Jupiter and Saturn rise around 9 p.m.
  • Mars rises around midnight and Venus at 3 a.m.
  • Mercury might be discernible low in the dawn glow, rising about 4 a.m.
  • The Moon will be full on the third.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



More Skywatching articles



226105
About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



230329
The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

Previous Stories



228921
231864


233351