"Fasten your seat belts — New Horizons has arrived at the Pluto System." Those were the words of Alan Stern, New Horizons' principal investigator, at this morning's briefing. After more than nine years and 3 billion miles, the spacecraft is inside the dwarf planet's Hill sphere of influence and ready to take the first detailed measurements and photographs of Pluto.
New Horizons is already well within 1 million miles of Pluto and is rapidly approaching the 31,000 mile per hour flyby that will bring it within 7,800 miles (about 12,500km). Below you'll find a schedule of what's happening when, as well as when NASA will be doing live streams of the events here at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. But first, if you're not sure why we're heading to Pluto in the first place, our sister site Vox has put together a wonderful 3-minute primer:
What have we learned so far?
The New Horizons team has already solved one of the biggest mysteries about Pluto: its size. This morning, NASA announced that Pluto is 2,370km (about 1,473 miles) in diameter, give or take 20m. That makes it ever so slightly bigger than Eris, a much darker and denser object that lives farther out in the Kuiper Belt. (Eris measures 2,336km in diameter.) Measurements of Pluto's size before today were estimates at best, their accuracy skewed by the dwarf planet's hazy atmosphere.
This morning also brought confirmation that Pluto has an icy polar cap, which is made of a mix of frozen methane and nitrogen gases. And while scientists had theorized that Pluto's thin atmosphere contained nitrogen, we've already learned that the gas is escaping Pluto's atmosphere much faster than expected.
What are we still unsure about?
A lot. The increasingly detailed views of the Pluto system have ramped up speculation about what geographic features might be found on its surface. A few of these were discussed in the morning briefing. Pluto may have a subsurface ocean, which could be evidenced by plumes escaping the planet — team scientists will be looking for those when New Horizons is behind Pluto looking back toward the Sun. While there are also a few large craters, Pluto's surface isn't as pockmarked as something like our Moon. That's a reflection of Pluto's more recent origins.
Many features are still to hard to resolve. For instance, the true nature of the large, black equatorial region is still unknown. There's also a mysteriously massive, white, heart-shaped region.
When will we see the Pluto system in high resolution?
NASA has been releasing incrementally better photos of Pluto and Charon for weeks now, but as New Horizons gets closer, the resolution of these photographs will increase exponentially. (The twitter bot NewHorizonsBot has been the best source for instant links to the newest uploads to the JUAPL server.) At around 11:15PM ET tonight, July 13th, the team will get a downlink from New Horizons that contains the best full-frame image from the black-and-white LORRI camera. (It will likely be released on the morning of the 14th, though.)
After this, New Horizons will "go dark" as it prepares for its flyby tomorrow morning. Because the spacecraft is zooming past instead of entering an orbit around Pluto, the spacecraft has to completely focus its instruments to take full advantage of its proximity. New Horizons will make that closest approach — about 12,500km (or 7,800 miles) — at 7:49AM ET.
The most recent color views of Pluto and Charon, its biggest moon. (Note: this image has been composited and does not reflect the true orbit.)
All signs point to the spacecraft hitting its tiny 100km-by-150km (60 mile-by-90 mile) flyby window, and Stern said there's only a one in 10,000 chance that it will be impacted by debris. Still, New Horizons is traveling at about 31,000 miles per hour, so making contact with any piece of debris of significant size would spell immediate doom for the probe. NASA TV will hold a live broadcast for these activities from 7:30AM ET until 9:00AM ET.
Here's the stressful part: we won't know for sure that New Horizons successfully completed the flyby until much later in the evening. If it has, the team should receive a tiny amount of data from the spacecraft at about 9:02PM ET.
Wednesday morning, at 7AM ET, team scientists will downlink the best full-frame image of Charon. We should also get a glimpse of Hydra, one of Pluto's other moons. And later in the day we should get what we have all been waiting for — the first high-resolution mosaic of Pluto will be released some time around 3:25PM ET.
Who should I follow?
- Alan Stern, New Horizon's principal investigator, who hasn't been shy about how his team still refers to Pluto as a planet.
- Mike Brown, the man behind the movement to remove Pluto's planetary status in the first place.
- Kimberly Ennico Smith, deputy project scientist for New Horizons.
- Dava Newman, NASA's new deputy administrator.
- Emily Lakdawalla, senior editor of The Planetary Society.
- Alex Parker, one of New Horizon's scientists involved with the imaging of Pluto.
- Sara Hörst, assistant professor of planetary science at Johns Hopkins.
- John Grunsfeld, NASA's science lead.
- Amy Shira Teital, NASA's social media correspondent for New Horizons.
- The official New Horizons Twitter account.
Full New Horizons schedule (with NASA's livestream info)
Tuesday, July 14th
- 7:30AM - 9:00AM ET: NASA TV coverage begins. Pluto and Charon images released.
- 7:49AM ET: New Horizons flies by Pluto at a distance of 7,800 miles away.
- 8:30PM - 9:10PM ET: NASA TV coverage of New Horizons' "phone home" from mission control.
- 9:02PM ET: New Horizons' scheduled data connection.
- 9:30PM - 10:00 PM ET: NASA TV coverage of a scheduled media briefing on the health and mission status of New Horizons.
Wednesday, July 15th
- 3:00PM - 4:00PM ET: NASA TV coverage of media briefing and high-resolution images of Pluto. An image of Nix, another one of Pluto's moons, will also be released.
Thursday, July 16th
- 12:24AM ET: New Pluto mosaic released.
- 3:24AM ET: Highest resolution mosaic image of Charon released.
- 9:23AM ET: Color image of Pluto and Charon orbiting each other released.
Friday, July 17th
- 12:33PM ET: Best-resolution photo of a fully lit Hydra, one of Pluto's moons.
Saturday, July 18th
- 6:30AM ET: Crescent photo of Pluto from its backside. Best color image of Nix, one of Pluto's moons.
Monday, July 20th
- 12:03PM ET: Final Pluto mosaic image downlinked until September.
Update 8:00PM, July 14th: The New Horizons team now expects to receive the signal at 9:02PM ET. This post has been updated to reflect the new time.