NIAC 2017: Interstellar Implications

I always look at the NASA Innovative Advanced Concepts (NIAC) awards with interest as well as a bit of nostalgia. When I began researching the book that would become Centauri Dreams, NIAC was an early incentive. Then known as the NASA Institute for Advanced Concepts, it was under the direction of Robert Cassanova (this was back around 2002), and its archive of funded studies was a treasure house of deep space ideas, from antimatter extraction in planetary magnetic fields to exoplanet imaging through starshades. I spent days going through any number of reports and interviewed many NIAC study authors.

You can still see the NIAC reports from that era on the older site (go to NIAC Funded Studies). The current NIAC site makes the point that the program looks for “non-traditional sources of innovation that study technically credible, advanced concepts that could one day ‘change the possible’ in aerospace.” And it’s here that we get the 2017 Phase 1 proposals, a $125,000 award for a nine month period that can result in a two-year Phase II follow-up.

Laser-Fed Ion Drive for Interstellar Precursor

2017 proposals with specifically interstellar intent include one from JPL’s John Brophy, who describes what he calls “A Breakthrough Propulsion Architecture for Interstellar Precursor Missions.” Brophy is looking for a way to deliver a high spacecraft velocity change (delta-V) without using much propellant. He envisions a lithium-fueled ion thruster with a specific impulse of 58,000 seconds (compare this with the Dawn spacecraft’s 3,000 seconds).

How to achieve this? By use of a 10-km orbital laser array that allows his craft to operate far beyond the point where sunlight loses its useful effect, the array feeding a lightweight, photovoltaic array aboard the spacecraft that can produce the electric power to drive the thrusters. Brophy believes laser power in this configuration can be converted to electric power at an efficiency of 70 percent, to produce an output voltage of 12 kV. The lithium fueled system would be capable of a 12-year flight-time to 500 AU, close to the point where gravitational lensing begins to get interesting. Time to Pluto: 3.6 years, and Jupiter in a single year.

So much depends upon that laser array, a ground-based version of which is under active study by the Breakthrough Starshot effort. The problems of implementing such an array are daunting, but its uses if ever built are so game-changing that the investigation continues. Breakthrough Starshot itself works with a 30-year horizon, so we are not talking about near-term implementation, but rather sketching out concepts a laser array could make feasible.


Image: Breakthrough Propulsion Architecture for Interstellar Precursor Missions
Credit: John Brophy.

Counting on Ernst Mach

Like Brophy’s proposal, Heidi Fearn’s “Mach Effects for In Space Propulsion: Interstellar Mission” is a Phase 1 initiative, an interesting entry because it shows NIAC beginning to open to the kind of breakthrough propulsion concepts NASA once investigated through its Breakthrough Propulsion Physics project (led by Tau Zero founder Marc Millis). In this case, the work goes toward a so-called Mach Effect Thruster (MET). Mach effects are transient variations in the rest masses of objects as predicted by standard physics where Mach’s principle applies. Proponents believe they offer the possibility of producing thrust without the ejection of propellant, as discussed in James Woodward’s Making Starships and Stargates: The Science of Interstellar Transport and Absurdly Benign Wormholes (Springer-Verlag, 2012).

What Fearn proposes is to investigate such thrusters by continuing the development of laboratory-scale devices while designing and developing power supply and electrical systems that will determine the efficiency of the Mach Effect Thruster. The analytical task is to improve theoretical thrust predictions and build a reliable model of the device. At the theoretical level, this team is definitely talking deep space, with part of the proposal being to:

Predict maximum thrust achievable by one device and how large an array of thrusters would be required to send a probe, of size 1.5m diameter by 3m, of total mass 1245 Kg including a modest 400 Kg of payload, a distance of 8 light years (ly) away.


Image: Mach Effects for In Space Propulsion: Interstellar Mission. Credit: Heidi Fearn.

Can such a device work? Remember, we are in the realm of advanced concepts, where the technology is at the TRL 1 level, but the benefits of working with a thruster that does not expel fuel mass could make high velocities possible, enough of an incentive to pursue these early steps. Mach’s principle relates the motion of the farthest objects in the universe to the local inertial frame or, as Hawking has it, “Local physical laws are determined by the large-scale structure of the universe.” The principle is vague enough that Hermann Bondi and Joseph Samuel have compiled eleven different variations on it, all of which could be called Machian.

Gravitational Lensing and Exoplanet Imaging

JPL’s Slava Turyshev is behind a Phase 1 study called “Direct Multipixel Imaging and Spectroscopy of an exoplanet with a Solar Gravity Lens Mission,” a study focusing on a mission to exploit the Sun’s gravitational lens, where (at 550 AU and beyond) the Sun’s gravity has bent the light of objects directly behind it to allow powerful lensing effects.

Long-time Centauri Dreams readers will know that the Italian physicist Claudio Maccone has championed a gravitational lens mission called FOCAL for many years, proposing it to the European Space Agency and writing numerous papers as well as two books on the topic (there is much available in the archives here about this concept). The definitive book, Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer, 2009) lays out the principles of such lensing, the history of its study, and potential solutions to the many imaging issues raised by a space mission. Maccone has discussed lensing as one solution to the communications challenges of Breakthrough Starshot.

What Turyshev is proposing is to study not the means of getting to 550 AU and beyond, but the question of spacecraft operations at such distances. From the proposal description:

Specifically, we propose to study I) how a space mission to the focal region of the SGL (Solar Gravitational Lens) may be used to obtain high-resolution direct imaging and spectroscopy of an exoplanet by detecting, tracking, and studying the Einstein’s ring around the Sun, and II) how such information could be used to unambiguously detect and study life on another planet.


Image: Direct Multipixel Imaging and Spectroscopy of an exoplanet with a Solar Gravity Lens Mission. Credit: Slava Turyshev.

Other proposals of interest are “Pluto Hop, Skip and Jump Global,” from Benjamin Goldman (Global Aerospace Corporation), an innovative study of a Pluto lander with a novel approach to landing and in situ science; “Gradient Field Imploding Liner Fusion Propulsion System” from Michael LaPointe (NASA MSFC), exploring magneto-inertial fusion in a new configuration that could lend itself to in-space propulsion; and “Fusion-Enabled Pluto Orbiter and Lander,” from Stephanie Thomas (Princeton Satellite Systems, Inc.), a Direct Fusion Drive concept based on work under development at the Princeton Plasma Physics Laboratory, and its application in a Pluto orbiter with lander (this one is a Phase II study).

The full list of 2017 Phase I and Phase II selections is here, including Nan Yu’s interesting take at JPL on possible dark energy interactions with a ‘Solar System laboratory.’ Have a look at these and ask yourself which we may still be talking about a decade hence. When I look back to the NIAC studies I examined in 2002 and later, I find many ideas that we wound up discussing at length here on the site, and I wouldn’t be surprised if several of the new selections move on to Phase II status and a great deal of future scrutiny. Which ones will they be?


Outer System News

NASA is to discuss new findings about ocean worlds in our Solar System in a news conference at 1400 EDT (1800 UTC) on Thursday. The prospects for oceans in the outer system are surprisingly varied, ranging from the strong evidence of a subsurface, salty ocean on Europa to other Jovian moons like Ganymede and Callisto, and of course, Saturn’s intriguing moon Enceladus. Titan is thought to have a salty ocean perhaps 50 kilometers below its ice shell, while there are also possible ocean venues on Mimas, Triton and even Pluto.

The news briefing participants will be:

  • Thomas Zurbuchen, associate administrator, Science Mission Directorate at NASA Headquarters in Washington
  • Jim Green, director, Planetary Science Division at NASA Headquarters
  • Mary Voytek, astrobiology senior scientist at NASA Headquarters
  • Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California
  • Hunter Waite, Cassini Ion and Neutral Mass Spectrometer (INMS) team lead at the Southwest Research Institute (SwRI) in San Antonio
  • Chris Glein, Cassini INMS team associate at SwRI
  • William Sparks, astronomer with the Space Telescope Science Institute in Baltimore

Further information and a link to view the news briefing can be found here, and the event will also be streamed live on YouTube.

Elsewhere in the Outer System

New Horizons is now in hibernation, a mode that will last until early September. While the spacecraft slumbers, the science and mission operations teams will be working on command loads for the flyby of Kuiper Belt Object MU69, planning for a nine-day encounter with closest approach on New Year’s Day of 2019. We’re now 38.15 AU from the Sun and 5.07 AU from Pluto, moving with a heliocentric velocity of 14.29 kilometers per second.


At Ceres, the Dawn spacecraft is in its extended mission and now studying the dwarf planet in a highly elliptical orbit. Later this month, the Sun will be directly behind the spacecraft, when it is at an altitude of about 20,000 kilometers. The strong lighting may help tease out new features about the surface, even as the primary science objective — to measure cosmic rays as part of the analysis of chemical elements near the surface — continues.

We’re also learning more about what appears to be a transient atmosphere around the dwarf planet. A new study points to the Sun as the source of the atmosphere’s intermittent nature. The paper, published in Astrophysical Journal Letters, makes the case that energetic particles from the Sun’s solar wind can free water molecules from the ground, producing an atmosphere, vanishingly thin, that may last for up to a week.

“Our results also have implications for other airless, water-rich bodies of the solar system, including the polar regions of the moon and some asteroids,” says Chris Russell (UCLA), principal investigator of the Dawn mission. “Atmospheric releases might be expected from their surfaces, too, when solar activity erupts.”

If this sounds like cometary behavior, with ice sublimating at the surface as the comet nears perihelion, the paper plays down the idea, noting that the activity does not seem timed to Ceres’ closest approach to the Sun. Lead author Michaela Villarreal (also at UCLA), adds that the team does not believe sublimation can explain the observed exosphere. Earlier detections of an atmosphere on Ceres coincided with higher concentrations of energetic particles from the Sun, and non-detections occurred at lower particle levels.

Thus solar activity rather than Ceres’ orbital position seems to be the cause. This leads to a prediction: Given that the Sun is now in a relatively quiet period that is expected to last for several years, the authors predict that we will see little atmosphere on Ceres during this time. This should be the case even though Ceres is currently getting closer to the Sun.

The evidence for ice on Ceres is strong, with the spacecraft’s gamma ray and neutron detector (GRaND) finding an uppermost surface rich in hydrogen and consistent with water ice; the ice is nearer to the surface at higher latitudes. Dawn has directly detected ice at Oxo crater and in one of the craters that are persistently in shadow in the northern hemisphere. And according to this JPL news release, we know that the shapes of craters and other surface features are consistent with water ice in Ceres’ crust.

Image: The dwarf planet Ceres overlaid with the concentration of hydrogen determined from data acquired by the gamma ray and neutron detector (GRaND) instrument aboard NASA’s Dawn spacecraft. The hydrogen is in the upper meter of regolith, the loose surface material on Ceres. The color scale gives hydrogen content in water-equivalent units, which assumes all of the hydrogen is in the form of H2O. Blue indicates where hydrogen content is higher, near the poles, while red indicates lower content at lower latitudes. In reality, some of the hydrogen is in the form of water ice, while a portion of the hydrogen is in the form of hydrated minerals (such as OH, in serpentine group minerals). The color information is superimposed on a shaded relief map for context. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

The evidence for a faint atmosphere on Ceres preceded Dawn’s arrival in 2015. As far back as 1991, the International Ultraviolet Explorer satellite found hydroxyl emission from Ceres, although no such emissions could be detected the year before. The European Space Agency’s Herschel Space Observatory likewise detected water in the possible atmosphere on three separate occasions, but was unable to find an atmopshere on the fourth attempt. The solar activity theory gives us a way to explain the transient nature of this thin atmosphere.

The paper is Villarreal et al., “The Dependence of the Cerean Exosphere on Solar Energetic Particle Events,” Astrophysical Journal Letters Vol. 838, No. 1 (24 March 2017). Abstract available.


The Value of an Exo-Venus

Looking back at science fiction’s treatment of Venus, you can see a complete reversal by the 1960s, at which time we had learned enough about the planet to render earlier depictions invalid, and even quaint. Think back to the inundated surface of Venus in Bradbury’s “Death by Rain” (1950) or Henry Kuttner and C. L. Moore’s Clash by Night (1943), where humans live under water and the land surfaces are carpeted with jungle. Heinlein’s Space Cadet is another example of a fecund Venus much like an Earthly rain forest.

But by 1965, Larry Niven would be writing “Becalmed in Hell,” about a nightmare Venus based on our insights into its intolerable surface. I should also mention a prescient tale by a writer who is a personal favorite of mine, James Gunn. It’s “The Naked Sky” (1955), which shows us a desert Venus with hydrochloric acid clouds and huge atmospheric pressure, a land Gunn described as “embalmed at birth.” As far as I know, this was the first SF tale that began to get Venus accurately, though at the time Gunn wrote, spacecraft had yet to confirm the hypothesis.

By 1962, we would have Mariner 2 readings of surface temperatures on Venus, while Soviet Venera probes would begin their work in 1967 with the first landing of a man-made object (Venera 4) on another planet. The program would continue for 16 launches, with 10 successful landings on the planet. Venera found a surface hot enough to melt lead, and survival times were short, with even the final iterations lasting no longer than about two hours.


Image: An image from the Soviet Venera 13 spacecraft. This was the first of the Venera missions to include a color TV camera and the first to succeed in obtaining pictures since Venera 10. Venera 13 lander touched down on 3 March 1982.

Now we’re finding planets much like Venus — or with the potential of being so — around other stars. With all the current interest in identifying an Earth 2.0, why be interested in Venus analogues? Elisa Quintana (NASA GSFC/SETI Institute), who works with the Kepler team, is one of the discoverers of such a world, Kepler 1649b. And here’s her take:

“Many people are hung up on finding other Earths. But Venus analogs are just as important. Since new telescopes coming down the pike will allow us to probe atmospheres, focusing on both Earth and Venus analogs may help decipher why, in our Solar System, one planet allows life to thrive, and one does not, despite having similar masses, comparable densities, etc.”

It’s a telling point, because the reason we got all those science fiction tales about a jungle Venus is that in so many ways it seemed to be a twin of the Earth, albeit one that was 40 percent closer to the Sun. It was easy to transfer tropical traits to the place, as if a journey there were somewhat like heading into unexplored equatorial terrain on our own planet.

Although Kepler 1649b circles a red dwarf star about 220 light years away, it receives about 2.3 times the stellar flux that the Earth does. The number for Venus is 1.9 times the terrestrial value. Looking into what makes Venus the nightmare it is can help us understand habitable zone boundaries around M-dwarfs that much better as we examine the tidal effects and stellar activity through flares and stellar wind that distinguish red dwarf planets from the Sun’s.

Follow-up spectroscopy and imaging of Kepler 1649 indicated to lead author Isabel Angelo (SETI Institute) and team that the parameters of the star had to be adjusted. It turned out to be considerably hotter and larger than had been thought, the adjusted figures affecting the planet observed in transit. We now know that Kepler 1649b is just slightly larger than Earth. This is another case where Kepler planets have been re-characterized because of revisions to the properties of the host star, and a reminder of the importance of such follow-ups.

We learn from all this that the planet is on a 9-day orbit, but it is too small to produce solid radial velocity data that would help determine its mass, leading the authors to make no conclusions about mass or composition. The likelihood, though, considering that Kepler 1649b is 1.08 times the radius of the Earth, is that we are dealing with a rocky world. The paper compares the planet to Kepler-186f, an Earth-sized exoplanet thought to orbit in the habitable zone of another M-dwarf. Flares and coronal mass ejections are factors around such stars, while tidal locking and heating could affect the geological activity on both. The authors consider the two to be good candidates for Earth- and Venus-analog studies.

From the paper:

The discovery of Kepler-1649b is part of a larger movement toward confirmation and characterization of a variety of Earth-sized exoplanets, with the ultimate goal of understanding what factors place constraints on habitability. Most of these planets have orbital periods measured to high precision, allowing us to calculate the flux received by the planet from its host star. As a result, determining the correlation between incident flux and atmospheric compositions would be highly useful in assessing the habitability of known exoplanets. More specifically, determining the compositions and atmospheres of planets like Kepler-1649b and Kepler-186f, two planets that together span a wide range of distances within the habitable zones of M-dwarfs, will be useful in understanding the nature of habitable zone boundaries for such star types. Future missions like K2, TESS, and JWST… will make these studies possible and therefore lend themselves to a better understanding of conditions required for exoplanet habitability.

Confirming what surface conditions are actually like on either world will demand spectroscopic analysis of their atmospheres, and when it comes to Venus analogues, this is a tricky proposition because of their opacity. But the paper adds that there are distinguishing features in the high clouds of Venus like carbon dioxide absorption and an upper haze layer with sulfuric acid, that could make detection possible. The thick atmosphere dominated by clouds also produces scattering and reflection effects that lead to high albedo, which the authors see as another piece of evidence that could link an atmosphere to a runaway greenhouse.

All such studies rely upon our confidence in the properties of the planets we find, and that means accurate information about their host stars. Missions like Gaia are designed to measure the distances to nearby exoplanet systems like Kepler-1649 through the most precise parallax measurements ever obtained, which should further tighten the parameters on systems like this one. We need to know more about the factors that can take two worlds of similar mass and density in our system and render one habitable while turning the other into a furnace.

The paper is Angelo et al., “Kepler-1649b: An Exo-Venus in the Solar Neighborhood,” Astronomical Journal Vol. 153, No. 4, published online 17 March 2017 (abstract and full text).


Atmosphere Detected around Super-Earth GJ 1132b

There’s interesting news this morning about planets around M-dwarfs. A team of astronomers led by John Southworth (Keele University, UK) has detected an atmosphere around the transiting super-Earth GJ 1132b. While we’ve examined the atmospheres of gas giants and have detected atmospheres on the super-Earths 55 Cancri e and GJ 3470 b, GJ 1132b is the smallest world yet where we’ve detected one. 39 light years from Earth in the constellation Vela, the transiting planet is 1.4 Earth radii in size, with a mass 1.6 times that of our world.

We’re continuing to move, in other words, into the realm of lower-mass planets when we study planetary atmospheres, an investigation that will be crucial as we look for biosignatures in distant solar systems. With GJ 1132b, we’re dealing with a planet too close to its star to be habitable (it receives 19 times more stellar radiation than the Earth does, and has an equilibrium temperature of 650 K, or 377° C). But finding a thick atmosphere here is encouraging given the level of flare and stellar wind activity on M-dwarfs.

Such activity could strip a planet of its atmosphere in some scenarios, so the survival of atmospheres on planets in the habitable zone of similar stars remains in play. In GJ 1132b, we have a planet whose atmosphere has evidently persisted for billions of years.

The GJ 1132b work was done with the GROND imager attached to the 2.2 m ESO/MPG telescope at La Silla. GROND (Gamma-ray Burst Optical/Near-infrared Detector) is normally used to study Gamma Ray Burst afterglows at seven different wavelengths from the optical to near-infrared, allowing rapid follow-up spectroscopic observations at other telescopes, but it can also be used to study exoplanets as well as optical, X-ray and radio transients.

Using GROND, the researchers could measure the decrease in brightness as the planet’s atmosphere absorbed some of the starlight while passing in front of the star in transit. The team’s intention was to determine the radius of the planet in each of the seven passbands (filters) for which it could obtain transit lightcurves, analyzing the significance of variations between the passbands in terms of atmospheric composition.

The result: The planet appeared larger at some wavelengths than others, an indication of an atmosphere opaque to specific wavelengths while transparent otherwise. The average radius of the planet could be separated out into a surface radius of 1.375 Earth radius overlaid by this atmosphere, which increases the observed radius at the wavelengths mentioned.

Simulating different atmospheres through follow-up work from team members at the University of Cambridge and the Max Planck Institute for Astronomy, Southworth and company found that an atmosphere rich in water and methane fit their observations. As to what the planet’s surface composition might be, two possibilities emerge. From the paper:

We find that the mass and radius are consistent with two broad compositional regimes. Firstly, an exactly Earth-like composition, with 33% iron, 67% silicates and no volatile layer, is inconsistent with the data within the 1? uncertainties. But, a composition with higher silicate-to-iron fraction, including a pure silicate planet, is ostensibly consistent with the data, albeit marginally.

So perhaps a rocky world, or perhaps not:

On the other hand, the data are also consistent with a large range of H2O mass fractions between 0% and 100% in our models. In principle, consideration of temperature-dependent internal structure models would lead to larger model radii for the same composition… and therefore could lower the upper limit on the water mass fraction. Nevertheless, the mass and radius of GJ 1132 b allow for a degenerate set of solutions ranging between a purely silicate bare-rock planet and an ocean planet with a substantial H2O envelope.


Image: Artist’s impression of the exoplanet GJ 1132 b, which orbits the red dwarf star GJ 1132. Credit: MPIA.

The authors advocate extensive follow-up work on this planet with instruments like the Hubble Space Telescope, ESO’s Very Large Telescope, and the James Webb Space Telescope. In particular, we can begin to delve into the atmosphere here to look for its constituents:

Intermediate-band photometry at 900 nm or bluer than 500 nm would enable finer distinctions to be made between competing model spectra and a clearer understanding of the chemical composition of the planetary atmosphere. The planet’s mean density measurement is also hindered by the weak detection of the velocity motion of the host star, an issue which could be ameliorated with further radial velocity measurements using large telescopes. Finally, infrared transit photometry and spectroscopy should allow the detection of a range of molecules via the absorption features they imprint on the spectrum of the planet’s atmosphere as backlit by its host star.

We’re getting close to the day when improved space- and ground-based installations will allow us to use transmission spectroscopy to look for biosignatures in the atmospheres of planets in the habitable zone of nearby red dwarfs, markers like oxygen, ozone, methane and carbon dioxide in a simultaneous presence that would indicate replenishment by living systems. We’re not there yet, but what we have here is a demonstration that a planet with 1.6 Earth’s mass in a tight orbit of its red dwarf host is capable of holding on to an extensive atmosphere.

The paper is Southwork et al., “Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132B,” Astronomical Journal Vol. 153, No. 4 (31 March 2017). Abstract / preprint.


New Horizons: Star Fields Beyond

The attitude you bring to a star field changes everything. When I was a kid trying to figure out how to use a small telescope, I scanned the usual suspects — the Moon, Saturn and its rings, the Galilean satellites of Jupiter — all the while planning to branch out into major wonders like M31 or the Ring Nebula in Lyra. But when I turned to deep sky objects, what I discovered was that I could see little more than faint smudges — I was using no more than a 3-inch reflector. It was a disappointment for a while, until I accepted the limitations of my equipment.

And then I became a cataloger of faint smudges, as avidly tracking down celestial objects as any stamp collector sorting through new finds. A patient uncle showed me how to look slightly away from the object I sought, to pick it up in peripheral vision. I began keeping notebooks listing my first glimpses of various nebulae and clusters. So many celestial objects were out of reach, but somehow a field of stars became wondrous not only for what I was seeing but for what I knew I might see with a larger instrument.

The image below recalled those days precisely because of what we cannot see in it. This is actually drawn from a series of images taken by New Horizons’ LORRI instrument showing the area toward which the craft is heading. We’re looking toward a close approach and flyby of the Kuiper Belt object MU69 at 0200 Eastern US time (0700 UTC) on New Year’s Day of 2019. Right now we’re still far enough way that the target isn’t visible even to LORRI, but to me this image is freighted with the raw excitement of exploration as we push ever deeper into the Solar System.


Image: In preparation for the New Horizons flyby of 2014 MU69 on Jan. 1, 2019, the spacecraft’s Long Range Reconnaissance Imager (LORRI) took a series of 10-second exposures of the background star field near the location of its target Kuiper Belt object (KBO). This composite image is made from 45 of these 10-second exposures taken on Jan. 28, 2017. The yellow diamond marks the predicted location of MU69 on approach, but the KBO itself was too far from the spacecraft (877 million kilometers) even for LORRI’s telescopic “eye” to detect. New Horizons expects to start seeing MU69 with LORRI in September of 2018 – and the team will use these newly acquired images of the background field to help prepare for that search on approach. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

New Horizons is going into hibernation this week for a 157 day period, and I hadn’t realized until getting this JHU/APL update that the craft had been in full operational mode for almost two and a half years now, which of course dates back to the Pluto encounter and the long period of data return (16 months). Along the way New Horizons has continued to study the dust and charged particle environment of the Kuiper Belt as well as hydrogen in the heliosphere.

We’re now halfway between Pluto and MU69, having reached this point — a distance of 782.45 million kilometers from Pluto and MU69 — early on April 3 (UTC). The gravitational pull of the Sun continues to slow the craft, so it won’t be until tomorrow (April 7) that we reach the halfway point in terms of time between the two close approaches. Remember that New Horizons left Earth orbit traveling faster than any vehicle ever launched, but nine years of climbing out of the gravity well have slowed it to 14 kilometers per second at the Pluto/Charon flyby, significantly below the 17 kilometers per second-plus that Voyager 1 has attained.

The good news is that the mission includes further exploration beyond MU69. Hal Weaver is a New Horizons project scientist from the Applied Physics Laboratory (Laurel, MD):

“The January 2019 MU69 flyby is the next big event for us, but New Horizons is truly a mission to more broadly explore the Kuiper Belt. In addition to MU69, we plan to study more than two-dozen other KBOs in the distance and measure the charged particle and dust environment all the way across the Kuiper Belt.”

Looking ahead once we’re past MU69, there will be so many things we cannot see in the star field ahead. So much to discover for the deep space missions beyond New Horizons. When will a true interstellar probe — a mission designed from the start to examine the local interstellar medium — be launched? Without an answer, we can only keep pushing for exploration, an innate characteristic of our species, and one unlikely to be limited by our Solar System.