Reply to post: Re: Uh, am I the only one

First low-frequency fast radio burst to grace our skies detected at last

Bill Gray

Re: Uh, am I the only one

"But we're detecting it at light years, which would imply a signal strong enough to be used at interstellar distance."

We're detecting _echoes_ from Mercury at interplanetary distances. Big difference. Radar detection drops as the _fourth power_ of distance; move an object ten times further away, and it collects 1/100 as many radar photons, and then you lose another factor of 100 on the way back. (Which is why almost all radar distance/range rate measurements are done on near-earth objects, only a few times further away than the moon; it takes a _big_ object for such measurements to work over longer distances, and _huge_ amounts of power.)

This is also why the folks tracking artificial satellites use radar for low-earth objects and optical observations for objects in higher orbits. At least for publicly released data, the US military satellite surveillance folks can track objects only a few centimeters across in low-earth orbit, about 350 km away. But an object orbiting as far away as the moon would have to be a few tens of kilometers across to return a similar signal.

If you were on a background star when the big interplanetary radars pinged (for example) Mercury, I _think_ you would get a series of pulses. You'd only see it once, though; the next time we pinged Mercury, it would have moved and some other aliens would get the signal.

POST COMMENT House rules

Not a member of The Register? Create a new account here.

  • Enter your comment

  • Add an icon

Anonymous cowards cannot choose their icon


Biting the hand that feeds IT © 1998–2019