Monday, June 14, 2010
Jupiter Impact: Mystery of the Missing Debris - On June 3rd, 2010, something hit Jupiter. A comet or asteroid descended from the black of space, struck the planet's cloud tops, and disintegrated, producing a flash of light so bright it was visible in backyard telescopes on Earth. Soon, observers around the world were training their optics on the impact site, waiting to monitor the cindery cloud of debris which always seems to accompany a strike of this kind. They're still waiting.
"It's as if Jupiter just swallowed the thing whole." "It was thrilling to see the impact, but the absence of any visible debris has got us scratching our heads." Indeed, it is a bit of a puzzle. "We've seen things hit Jupiter before, and the flash of impact has always been followed by some kind of debris." So where is the debris this time?
A possibility offered by some observers is that the flash wasn't an impact at all. Maybe it was a giant Jovian lightning bolt. But "NASA spacecraft have seen lightning on Jupiter many times before, but only on the planet's night side. This day side event would have to be unimaginably more powerful than any previous bolt we've seen. Even Jupiter doesn't produce lightning that big."
Curiously, the impactor (if indeed this was an impact event) struck right in the middle of Jupiter's South Equatorial Belt (SEB), one of the two broad stripes that girdle the planet. This is "curious" because the SEB itself vanished earlier this year. The missing belt may still exist, just temporarily hidden underneath some high-altitude cirrus clouds.
The best remaining hypothesis is that the impactor was small, packing just enough punch to make a flash, but without leaving much debris. One thing is sure: "JUPITER IS GETTING HIT MORE THAN WE EXPECTED. Back in the days of Shoemaker-Levy 9 (SL-9), we calculated that we should see an impact on Jupiter once every hundred years or so. We considered ourselves extraordinarily lucky to witness the SL-9 event. But look where we are now. Anthony Wesley has observed two impacts within the past 12 months alone. It's time to revise our impact models
HOW TO READ PROPAGATION NUMBERS
The A index [ LOW is GOOD ]
- 1 to 6 is BEST
- 7 to 9 is OK
- 11 or more is BAD
Represents the overall geomagnetic condition of the ionosphere ("Ap" if averaged from the Kp-Index) (an average of the eight 3-hour K-Indices) ('A' referring to amplitude) over a given 24 hour period, ranging (linearly) typically from 1-100 but theoretically up to 400.
A lower A-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Ap-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
SFI index [ HIGH is GOOD ]
- 70 NOT GOOD
- 80 GOOD
- 90 BETTER
- 100+ BEST
The measure of total radio emissions from the sun at 10.7cm (2800 MHz), on a scale of 60 (no sunspots) to 300, generally corresponding to the sunspot level, but being too low in energy to cause ionization, not related to the ionization level of the Ionosphere.
Higher Solar Flux generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; Solar Flux rarely affects the 30, 40, 60, 80, & 160 Meter Bands.
K index [ LOW is GOOD ]
- 0 or 1 is BEST
- 2 is OK
- 3 or more is BAD
- 5 is VERY VERY BAD
The overall geomagnetic condition of the ionosphere ("Kp" if averaged over the planet) over the past 3 hours, measured by 13 magnetometers between 46 & 63 degrees of latitude, and ranging quasi-logarithmically from 0-9. Designed to detect solar particle radiation by its magnetic effect. A higher K-index generally means worse HF conditions.
A lower K-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Kp-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
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