# Could we detect an alien starship entering Earth's Solar System? Or in it?

**URL:** <https://boards.straightdope.com/t/could-we-detect-an-alien-starship-entering-earths-solar-system-or-in-it/460840>\
**Category:** In My Humble Opinion\
**Created:** [August 21, 2008, 7:59pm UTC](https://boards.straightdope.com/t/could-we-detect-an-alien-starship-entering-earths-solar-system-or-in-it/460840 "2008-08-21T19:59:22Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![appleciders](https://avatars.discourse-cdn.com/v4/letter/a/85f322/32.png) [@appleciders](https://boards.straightdope.com/u/appleciders)\
**Post date:** [August 22, 2008, 5:58pm UTC](https://boards.straightdope.com/t/could-we-detect-an-alien-starship-entering-earths-solar-system-or-in-it/460840/21 "2008-08-22T17:58:32Z")

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I think we could detect #1 fairly easily if we happened to be looking in that direction. Given the amount of time it would take for that sort of “drive” to slow a massive interstellar ship, we’d probably be looking in the right direction at least once.

#2 might be detectable if the Bussard collection scoop was visible in itself or caused a visible effect. Most Bussard ramjet designs use a large magnetic scoop to magnetically accelerate hydrogen from a volume several kilometers in radius in towards a small fuel intake, and this might cause the hydrogen to emit light of some wavelength, which someone who’s taken more chemistry than I have could tell you.

Of course, if the ramscoop itself has mass and a relatively high albedo, it might be large enough to be visible. Then again, if we’re talking about a massive net with a high albedo surrounding a ship, we’re basically talking about a solar sail, which would probably be visible if aimed directly at us and might or might not otherwise.

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**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\
**Post date:** [August 22, 2008, 6:31pm UTC](https://boards.straightdope.com/t/could-we-detect-an-alien-starship-entering-earths-solar-system-or-in-it/460840/22 "2008-08-22T18:31:05Z")

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Radio telescope applications for Types #2 & #3?

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