4 ms·

So how long till next arm?

• blauditore 9y ago
  I don't know where we stand now, but there are two arms and a galactic year is ~250 million terrestrial years, so I'd say a priori on average ~250/2/2 = ~60 million years from now.
  • fastball 9y ago
    Probably better to take the average of the last known extinction events and extrapolate from there. Average time between events: 96 Myr. Time since last event: 33 Myr. Time to next event: 63 Myr. Wow, surprisingly close to your method. Pack up your bags boys, we're gonna get extincted in 60 million years.
  • vorg 9y ago
    There are two thick arms, and two thin ones in the picture, as well as a spur (the Orion Spur in which our Sun presently dwells). The article postulates the existence of a second spur on the far side of the galaxy where we can't see, based on the history of extinction events in the past 250 million years and the observed symmetry of many other spiral galaxies.
• mkempe 9y ago
  There are two danger periods: passing through the galactic plane (duration 100k years every 35Myr) and passing through the galactic arms (duration 10Myr every 120Myr). The article only discusses passage through the arms. We're currently moving away from the galactic plane, which our solar system last crossed 3Myr ago. According to the article there are 11 extinction events spread across the last 500Myr, which corresponds to two orbits of our solar system around the galaxy but one traversal through the arms and spur (they're also orbiting, more slowly). Right now we're in the Orion Spur; the authors seem to attribute an extinction phase near the last exit from this spur; the spur is 1 kly across, so I estimate our solar system takes 3 Myr to transit the width of the spur. I think our next destination is the Perseus Arm, 6.5 kly away, so we should reach it in about 20 Myr.