New Horizons is getting close to Pluto. Pluto and Charon have enlarged from featureless dots into worlds. Pluto's surface clearly bears streaks and splotches, while Charon is beginning to show the first hints of discernible features. Excitement is building for flyby day, July 14!

Key places to watch for New Horizons information:

Three months ago, I posted an article explaining what to expect during the flyby. The following is a revised version of the same post, with some errors corrected, the expected sizes of Nix and Hydra updated, and times of press briefings added.

UPDATE July 8: Added newly scheduled July 15 press briefing.

UPDATE July 12: Changed schedule of July 13 press briefing.

UPDATE July 14: Changed schedule of July 14 evening press briefings.

As New Horizons approaches, every image of Pluto and Charon that each instrument returns will be the best it has ever taken. All of these images will be thrilling to see. But until mid-July, all the images will still be pretty small. When will we get pictures that really answer questions about Pluto? In this blog entry I'll try to explain when we'll get the images that you're hoping for. First, the executive summary:

Closest approach is at 11:49:57 UTC / 07:49:57 EDT / 04:49:57 PDT on Tuesday, July 14, 2015.

New Horizons gets 1.2 million kilometers closer each day.

New Horizons has two cameras.

The Long-Range Reconnaissance Imager (LORRI) has a field of view of 0.29 degrees and a pixel scale of 4.94 microradians and takes black-and-white ("panchromatic") images.



The Ralph Multispectral Visible Imaging Camera (MVIC) has a field of view 5.7 degrees wide and a pixel scale of 19.77 microradians and takes both panchromatic and color images. It has panchromatic, near-IR, red, blue, and methane filters, but no green filter. Color images are usually IR/red/blue.

Today, June 24, is the last day that the orbit of Hydra fit within the LORRI field of view. Images containing Pluto may not contain all the other moons.

Through July 12, New Horizons will take regular LORRI photos of Pluto, Charon, Nix, and Hydra, which will mostly be returned soon after acquisition because they are used for optical navigation.

Pluto will appear larger than the LORRI field of view for less than 24 hours around closest approach.

Since Pluto and Charon rotate slowly (once every 6.4 days), all of the best fully-lit images will show the same hemisphere. The other hemisphere will be imaged at a best resolution of about 38 kilometers per pixel, 3.2 days prior to closest approach.

Pluto's axis is highly tilted, like Uranus, and it is currently summer in the northern hemisphere. All approach images will contain the sunlit north poles of Pluto and its satellites.

There are few data downlinks near closest approach, so we will not receive many images in real time. But the ones we get will be great.

The mission has promised to release LORRI images (higher-resolution, black-and-white) in near-real-time, but not MVIC (lower-resolution, color) images.

Only 1% of the science data from the flyby will be returned to Earth during the period around closest approach, including images that the mission has selected for their high science value as well as high public interest. They will be releasing captioned and processed versions as fast as their small team can manage.

The rest of the image data will be downlinked beginning in September, about 2 months after encounter. It will take 10 weeks to download the full data set.

It's hard to get data from Pluto

Data will arrive on Earth in a series of downlinks. Downlink sessions can last as long as about 8 hours, but are usually somewhat shorter. Whenever New Horizons is downlinking data, it can't take new photos, so the downlinks get shorter and less frequent as the spacecraft gets close to the time of the flyby, when it concentrates on collecting as much data as possible. Because data downlinks are slow, there will be much less data downlinked than New Horizons has stored on board. After data is downlinked, it must be processed before posting online. How long that will take is not yet known.

On Sunday, July 12, New Horizons will transmit the last of its optical navigation data. Then, on Sunday and Monday, July 12 and 13, there will be a series of four "Fail Safe" downlinks. These are designed to return a minimum set of data from all instruments, just in case New Horizons does not survive the flyby. A last downlink ending overnight Monday July 13, called "E-Health 1," will include one last pre-closest approach photo of Pluto.

Then there is a nail-biting 24-hour period of waiting while New Horizons concentrates on flyby science and does not communicate with Earth, followed by the much-anticipated beep of the "Phone Home" downlink on Tuesday night, July 14. Following closest approach, on Wednesday and Thursday, July 15 and 16, there will be a series of "First Look" downlinks containing a sampling of key science data. Another batch of data will arrive in the "Early High Priority" downlinks over the subsequent weekend, July 17-20. Then there will be a hiatus of 8 weeks before New Horizons turns to systematically downlinking all its data. Almost all image data returned during the week around closest approach will be lossily compressed -- they will show JPEG compression artifacts. Only the optical navigation images are losslessly compressed.

The transmission of the High Priority data set will be complete on July 20, and then image transmission will pause. For nearly two months, until September 14, New Horizons will switch to near-real-time downlinking of data from other, so-called "low-speed" instruments while it transmits just housekeeping information for all of the rest of the data. No new images will arrive on the ground during this time. I asked Kim Ennico for a little more explanation of the "low-speed" distinction, and she said: