One important caveat: the times reported above are when the images will be downlinked. This is not the same as when they will be published. New Horizons (unlike Curiosity, Opportunity, InSight, solar missions, and formerly Cassini) doesn't push images straight to the Web once they land on Earth. The mission will process them, and the team will write captions, and then NASA will have to vet the captions, and then NASA will publish the images at a time of day that'll maximize news coverage, all of which means it could be up to a day or so after downlink that these images get released.

Here are some of the best ways to keep up with the mission:

And now, a detailed look at all the plans for the mission to MU69.

Mission Design

In addition to the LORRI and MVIC cameras, New Horizons has several other science instruments. Remote sensing instruments include LEISA (which, together with MVIC, make up the Ralph instrument). LEISA takes spectra in infrared wavelengths. Alice is an ultraviolet spectrograph that can measure composition and also do stellar occultations to look for a coma around MU69. New Horizons also has three in-situ instruments for measuring fields and particles: the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), Solar Wind Around Pluto (SWAP); and the Student Dust Counter (SDC).

Mission planners have split the flyby into three main phases:

Currently, we are in the Approach phase, which began on 16 August and runs through 24 December (7 days before closest approach). During approach, New Horizons has been taking images for optical navigation and searching for potentially dust-generating hazards like rings or moons. (So far, it has not spotted any.) The in-situ instruments have been busy gathering data on the fields and particles in interplanetary space.

phase, which began on 16 August and runs through 24 December (7 days before closest approach). During approach, New Horizons has been taking images for optical navigation and searching for potentially dust-generating hazards like rings or moons. (So far, it has not spotted any.) The in-situ instruments have been busy gathering data on the fields and particles in interplanetary space. The Core phase will last 10 days, from 24 December to 2 January. Nearly all of the science will happen in just a 2-day period around closest approach, with intense imaging and spectroscopy to map MU69, study its composition, figure out its rotation rate and pole, and search for dust, rings, and satellites.

phase will last 10 days, from 24 December to 2 January. Nearly all of the science will happen in just a 2-day period around closest approach, with intense imaging and spectroscopy to map MU69, study its composition, figure out its rotation rate and pole, and search for dust, rings, and satellites. The Departure phase lasts one more week, from 3 through 8 January. After that, New Horizons will spend 20 months downlinking all the data, until September 2020.

A Challenging Encounter

Several things will make the MU69 flyby significantly more difficult than the Pluto flyby. MU69 is small, dark, and faint. New Horizons won’t see it as more than a dot until 3 days before closest approach. MU69 is darker, and the sunlight dimmer, than the LORRI camera was designed for. Also, because MU69 is so small, New Horizons has to pass much closer to it than it did at Pluto in order to see interesting detail on the surface, resulting in a rapidly changing viewpoint near closest approach.

As a result of all of these factors, LORRI’s images may be a little smeared and will be noisier than we saw at Pluto. MVIC is less affected by these challenges; the way that MVIC works, it’s possible for New Horizons to compensate for the low light and high speed by sweeping more slowly across MU69 to build up a stronger signal.

Another significant challenge arises from the fact that MU69 was only discovered in 2014. We don’t have a very long observational arc on its orbit around the Sun. So navigators don’t have as precise information as they’d like to have on its position. In particular, our knowledge of the position of MU69 along the line of sight from Earth is uncertain by several thousand kilometers. While New Horizons is approaching MU69 at a distance, it’s seeing the target at the same perspective that we do from Earth; New Horizons isn’t getting much parallax to refine our knowledge of exactly how far away it is along New Horizons’ line of sight. As New Horizons gets closer, the uncertainty in MU69’s position becomes a significant issue, because the real position of the body may be completely outside the field of view of a photo focused on the predicted position. In order to make sure it doesn’t miss the target, the spacecraft will have to scan its instruments across a region of space in which it is most likely to find the tiny world, taking a lot of data on empty space to make sure to get data on the object.

Core Phase

Have I mentioned yet that 2014 MU69 is small and faint? Even when New Horizons is just 3 days away from encounter, it will still only appear as one pixel to the sharpest-eyed camera, LORRI. So nearly all of New Horizons’ time through 28 December will be spent snapping photos for optical navigation, one set of images per day, and turning back to send them to Earth. It’s only in the final days before the flyby that New Horizons will see the world shift much against background stars, helping navigators to reduce the uncertainty in MU69’s position. Their final opportunity to update the pointings of LORRI images will be about 3 days before closest approach.

Late in the day on 29 December, they’ll start taking more science data. (By the way, these dates are all UTC according to the spacecraft’s clock. Because of the 6-hour one-way trip from New Horizons to Earth for radio signals, the time on the spacecraft’s clock matches the time of day in the U.S. Central time zone when we’ll be receiving the data, right in between Eastern and Pacific time -- so it’s “late in the day on 29 December” for those of us in the U.S., too. Handy for me!) Some long-exposure image sets will search for satellites. They’ll do “plasma rolls” to orient the in-situ instruments in all directions, characterizing the fields and particles as they get close. Shorter-exposure imaging will start gathering resolved images of MU69, but it will still only be barely larger than a LORRI pixel.

Toward the end of 29 December, science data gathering will really begin. A dense set of observations will gather a lightcurve on MU69, a measure of how its surface appears to change with rotation, over a period of about 6 hours. Prior imaging will have given hints of MU69’s rotation rate and pole direction, but these will be the first dense set of lightcurve data that should really help nail down those orbital characteristics. Is MU69 a fast rotator or slow rotator? Is it pointing a pole at the Sun, or are we seeing it sideways? We don’t know yet and we won’t really find out until those data land on Earth. Color images will start in order to see if MU69’s color varies with longitude, but MVIC won’t be able to resolve MU69 as more than a pixel yet.

Next, 30 December will see another 6-hour block of science, a mix of color imaging, deep satellite searches, and lightcurve data. The same happens early on 31 December, after which New Horizons enters the most intense, Inner Core phase of the flyby. New Horizons’ last communication phase with Earth will wrap up at 14:47 UTC according to the spacecraft clock on 31 December, or 20:55 UTC back here on Earth. The last images we receive will show MU69 as just a couple of pixels. Then, we wait.

Closest approach happens on 1 January at 05:33 according to the spacecraft’s clock, but it won’t be talking to us at the time.

Our first indication of how things went will arrive on Earth on 1 January at 15:28 UTC, or a very pleasant 10:28 in the morning in the Eastern time zone where the mission will be operating. There’ll be a quick “phone home” conveying spacecraft health, but no science data.

The first science data begins arriving later the same day, at 20:15 UTC (15:15 EST). The four-hour downlink should include a photo that is about 100 pixels across (see the simulation at the top of this post). Alan Stern calls these first downlinks the “New York Times” or “NYT” downlinks because he’s trying to bring down data that is valuable both scientifically and for public communication about the mission.

The second batch of science data will begin arriving on 2 January at 01:55 UTC (1 January at 20:55 EST). There might be a 200-pixel image in this downlink -- or maybe not. It depends where MU69 actually was. If it’s not in this downlink, it will hopefully be in a second image from the same observation that will hopefully arrive on Earth during the downlink that begins on 2 January 16:44 UTC (11:44 EST).

Here’s a detailed timeline of the above in several local time zones. SCET is "Spacecraft Event Time," the time according to the spacecraft's clock. All other times are "Earth Received Time," when we receive the signal from the spacecraft.