Pluto in a Minute: How Did New Horizons Phone Home?


By: NASA New Horizons

Originally published on Jul 15, 2015

New Horizons phoned home! But how exactly does a spacecraft talk to us from 3 billion miles away? This is Pluto in a Minute.

After being silent for nearly 22 hours on July 14, as planned, New Horizons did send a status report back to the mission team to let them know that the spacecraft was ok. But how does a signal travel to Earth from Pluto and how long does it take?

New Horizons sends and receives data on radio waves, which are the waves on the long end of the electromagnetic spectrum. Because they’re on the electromagnetic spectrum, radio waves travel at the speed of light. It takes sunlight about 8.3 minutes to travel 1 astronomical unit or 1 AU, that is, the distance between the Sun and the Earth. Pluto is currently about 32 AU from Earth, so 32 times 8.3 is about 265 (minutes). So the one way light time delay for the mission team to talk to New Horizons is about 4 and a half hours each way.

The signal left the spacecraft at about 4:27 in the afternoon on July 14. Traveling at the speed of light, that phone home signal crossed Neptune’s orbit about 25 minutes later. Then the signal traveled about hour and 28 minutes before crossing Uranus’ orbit. The signal reached Saturn’s orbit about hour and 28 minutes later, and then crossed Jupiter’s orbit another 28 minutes after that. Then an additional 33 minutes for the signal to reach Mars’ orbit, and then 7 minutes for it to go from Mars to the Earth.

And in the time that it just took me to explain exactly when that phone home signal crossed the planets’ orbits, a signal from or to New Horizons would not have moved very much at all.

For more on Pluto be sure to check out the New Horizons websites and also tweet your questions using the hashtag #PlutoFlyby. And of course, come back tomorrow for more Pluto in a Minute.

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