I’m sure you remember New Horizons’ encounters with Pluto in 2015 (“We have telemetry with the spacecraft!”) and Arrokoth in 2019 (“It’s a snowman!”) and how much fun those were. It seemed we’d have to wait a long time to hear from New Horizons again, and although the next flyby is a ways off, it’s done something very cool in the interim.
New Horizons is now sending us pictures from so far away (46.61 astronomical units, or 4,333,000,000 miles) that the nearest stars actually appear to be in different positions. This is the first parallax experiment ever done from somewhere other than Earth.
Usually we have to rely on the Earth’s motion around the Sun to use parallax. Nearby stars to appear to wobble more than faraway stars. Here is a ridiculous exaggeration of that, just to make it obvious:
You can intuitively tell which stars are close and which are far away
We know the diameter of our orbit, so we can use some geometry to figure out the distance to nearby stars this way.
The closest star to our Sun is Proxima Centauri, and we already know that its distance from us is 4.3 light-years (25,000,000,000,000 miles). New Horizons, then, is 0.017% as far away as that. It may not sound like much, but it’s enough to make Proxima Centauri, ANOTHER STAR, appear to shift its position.
“It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth,” said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado. “And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.”
Here are two images, one from Earth, and one from New Horizons, carefully aligned. Proxima Centauri is the only star that appears to move:
Proxima Centauri appears to change position relative to the other faraway stars. It feels almost closeby!
Here’s New Horizons’ path and where the planets are located tonight (June 12):
Where things are tonight in the Solar System, including New Horizons (at the end of the blue line, with the red line its future path)
So New Horizons is off a bit to the right of Jupiter, Saturn, and Pluto. Let’s see where those planets are in relation to Proxima Centauri in the sky. It’s easier to find Alpha Centauri (the big dog, also known as Rigil Kentaurus) on the sky map and just know that Proxima Centauri is really close to it:
Purple dots are Saturn, Jupiter, and Pluto. Green circle is around Alpha Centauri (aka Rigil Kentaurus).
The grid in the picture marks the borders of the constellations, but you can think of it as a glass planet Earth that we can see through. Alpha Centauri is down south, so we can’t see it from up here in the Northern Hemisphere. But right now you CAN see Jupiter and Saturn well above the horizon after midnight, close together in the sky because they’re in nearly the same place in their orbits, as you can see from the New Horizons Full Trajectory picture.
We said New Horizons was a bit to the right of the three planets shown (purple dots). So if you started to fly that way, you can imagine that if you looked down at Alpha Centauri (in the green circle), it’d start to appear to drift off to your right a little, and that’s what we see in the photo.
There’s also a comparison for a star called Wolf 359 (at 7.9 light-years), which appears to move less because it’s farther away:
Parallax data for Wolf 359, 7.9 light-years away
We sometimes imagine flying through space at “warp speed” and seeing stars go by. Those of us who grew up with snow in the winter would pretend our car was a spaceship as snowflakes flew past the windshield. Up to now that has been entirely imaginary, but this is the first glimpse we little humans have actually had of it for real. I think it’s amazing!
It’s fitting that Proxima Centauri is in our sights right now, because we’ve recently learned some intriguing things about it. Just recently it was confirmed that this little star, so close to us, has an Earthlike planet called “Proxima b” orbiting it in the habitable zone; that is, where liquid water can exist. That doesn’t mean there's life of any kind there … but neither does it mean there isn’t.
Recently, too, we have gotten what is likely a direct image of a confirmed second planet orbiting Proxima Centauri, “Proxima c”, which is much larger and may have rings:
From April 2018 data, published in April 2020. The bright spot in the “April 2018” circle is exactly where Proxima c was expected to be at that time based on its orbit; the “April 2020” circle shows where it was expected to be 2 years later to give the viewer a grasp of the orbital characteristics. Proxima Centauri is at the center, covered with a black dot to block its light. The identity of the bright spot as Proxima c remains to be confirmed.
We’re getting to know our closest stellar friend in the Universe better and better. Hey, if we drove there at 60 mph, it would only take 48 million years. Road trip!
In 2021, it will be up to Congress and President Biden to approve further funding of New Horizons, so that it can search for its own next flyby object, somewhere out in the Kuiper Belt. Joe won’t let us down.
New Horizons certainly hasn’t!
