And now for something a little different....
We sometimes spot comets over on Solar Stormwatch
. Here are a couple of celebrities:
|Comet McNaught:||Comet Machholz 96P|
Unlike these two most of the comets we see are usually from the Kreutz sungrazer group
, fragments from a large comet that broke up hundreds of years ago all thrown into orbits which take them on a one-way journey to the Sun. A few weeks ago on 1 October the STEREO
cameras watched as a particularly bright Kreutz comet disappeared into the glare of the Sun. SOHO-2143’s demise was not an unusual event – being vaporised in the fierce heat of the Sun’s atmosphere is the fate of all Kreutz group comets. The interesting thing about SOHO-2143 disappearance was what happened next. A huge solar storm (Coronal Mass Ejection or CME) blasted out from the opposite side of the Sun. So what do you think? Cause and effect or a coincidence timed to perfection? Have a look for yourself:
STEREO ahead camera.
Click on the picture to link to the mpg.
You'll find more video formats here
There are other examples too. Here's one
from earlier this year in May. Coincidence? The pseudo-science community love this kind of thing but what about the facts? Well, sungrazers are just that – they pass very close to the Sun rather than crash into it. So close they vaporise in the heat. Besides, comets are very loose collections of ice and rock – and tiny (less than 100m in diameter) compared to the Sun. This Solar Dynamics Observatory video
shows the scale of a (different) comet v Sun nicely. View this full screen and look for a pale streak moving very fast right to left about half way down.
Also there are 3 CMEs in the October video and only the third coincides with the disappearance of SOHO-2143. In short, no-one has found any evidence that the destruction of a sungrazing comet triggers a CME. That doesn’t mean people have stopped looking.
A typical CME is a billion tons of material travelling at a million miles an hour and contains mainly protons and electrons with some heavy ions. Outside the Earth’s thick protective magnetosphere these charged particles are a radiation hazard to any spacecraft and astronauts. Any manned lunar or Mars missions must, therefore, take this into account. Inside the Earth’s magnetosphere, the charged particles interact with the magnetic field producing geomagnetic storms, which in turn enhance the activity in the Earth’s radiation belts. This presents a radiation hazard to low-Earth orbit satellites and the astronauts on the ISS as they pass through the South Atlantic Anomaly
. In addition, electric currents generated by geomagnetic storms can cause electrical surges through power lines and damage power grids.
It is, therefore, important to be able to predict the speed and direction of CMEs but they are poorly understood and no-one really knows what triggers them. Data from Solar Stormwatch
are being used to track solar storms and learn more about how they begin and how they evolve.
Meanwhile, until a link is found between doomed comets and CMEs the conclusion is that it’s nothing more than an intriguing coincidence.
The exciting thing about the comet data from Solar Stormwatch is that it is about to be used to study particle sizes in comet tails. This will involve looking at absorption spectra as the tails drift across background stars and then comparing the results with infrared observations from the Herschel space observatory. This will also tell us more about the kind of dust and particles that are constantly battering the STEREO spacecraft!
More info:SOHONASABad Astronomy
- with Phil Plait's excellent video showing SOHO-2143 from 3 different perspectives