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Ultima Thule Flyby Approaches

by Paul Gilster | Dec 31, 2018 | Missions | 22 Comments

Despite the various governmental breakdowns attendant to the event, the New Horizons flyby of Ultima Thule is happening as scheduled, the laws of physics having their own inevitability. Fortunately, NASA TV and numerous social media outlets are operational despite the partial shutdown, and you'll want to keep an eye on the schedule of televised events as well as the New Horizons website and the Johns Hopkins Applied Physics Laboratory YouTube channel. Image: New Horizons' path through the solar system. The green segment shows where New Horizons has traveled since launch; the red indicates the spacecraft's future path. The yellow names denote the Kuiper Belt objects New Horizons has observed or will observe from a long distance. (NASA/JHUAPL/SwRI). We're close enough now, with flyby scheduled for 0533 UTC on January 1, that the mission's navigation team has been tightening up its estimates of Ultima Thule's position relative to the spacecraft, key information when it comes to the...

Exoplanet Imaging from Space: EXCEDE & Expectations

by Paul Gilster | Dec 26, 2018 | Exoplanetary Science | 56 Comments

We are entering the greatest era of discovery in human history, an age of exploration that the thousands of Kepler planets, both confirmed and candidate, only hint at. Today Ashley Baldwin looks at what lies ahead, in the form of several space-based observatories, including designs that can find and image Earth-class worlds in the habitable zones of their stars. A consultant psychiatrist at the 5 Boroughs Partnership NHS Trust (Warrington, UK), Dr. Baldwin is likewise an amateur astronomer of the first rank whose insights are shared with and appreciated by the professionals designing and building such instruments. As we push into atmospheric analysis of planets in nearby interstellar space, we'll use tools of exquisite precision shaped around the principles described here. by Ashley Baldwin This review is going to look at the current state of play with respect to direct exoplanet imaging. To date this has only been done from ground-based telescopes, limited by atmospheric turbulence...

The Essence of the Human Spirit: Apollo 8

by Paul Gilster | Dec 21, 2018 | Missions | 44 Comments

Looking Ahead

by Paul Gilster | Dec 18, 2018 | Administrative | 23 Comments

Centauri Dreams posts will unfortunately be sporadic over the next couple of weeks as I attend to some unrelated matters. But I do have several excellent upcoming articles already in the pipeline, including Al Jackson on Apollo 8 at the end of this week. Al, you'll recall, was involved in Apollo as astronaut trainer on the Lunar Module Simulator, so his thoughts on the program's extraordinary successes are always a high point. Image credit: Manchu. Ashley Baldwin, who knows the ins and outs of space-based astronomy better than anyone I know, will be looking at the key issues involved, with specific reference not only to WFIRST and HabEX but also a mission called EXCEDE, not currently approved but very likely the progenitor of something like it to come. In early January, Jim Benford will be talking about beamed propulsion in a two-part article that looks to resolve key particle beam issues, with methods worked out by himself and the ingenious Alan Mole. There are all kinds of...

Climate Change and Mass Extinctions: Implications for Exoplanet Life

by Paul Gilster | Dec 14, 2018 | Uncategorized | 95 Comments

The right kind of atmosphere may keep a planet habitable even if it crowds the inner region of the habitable zone. But atmospheric evolution involves many things, including the kind of geological activity our own planet has experienced, leading to sudden, deep extinctions. Centauri Dreams regular Alex Tolley today takes a look at a new paper that examines the terrestrial extinction of marine species in the Permian event some 252 million years ago. As we examine exoplanet habitability, it will be good to keep the factors driving such extinctions in mind. Tolley is a lecturer in biology at the University of California and author, with Brian McConnell, of A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer, 2016). A key question in his essay today: Is our definition of the habitable zone simply too broad? by Alex Tolley In the search for life on exoplanets, questions about whether the planet is within the HZ given a plausible atmosphere is based on...

Early Returns from Bennu

by Paul Gilster | Dec 12, 2018 | Asteroid and Comet Deflection | 12 Comments

The science return from OSIRIS-REx has been surprisingly swift as the spacecraft returns data on near-Earth asteroid 101955 Bennu. We're aided here by the timing, as early results are being discussed at the ongoing conference of the American Geophysical Union (AGU) in Washington, DC. The imagery we've received of Bennu's surface has scientists buzzing. Thus Humberto Campins (University of Central Florida) a member of the OSIRIS-REx Science Team, who notes the comparison between what we see now and the Arecibo radar imagery in the late 1990s: "The images are spectacular and spot on, what we expected thanks to predictions made with the instrumentation at the Arecibo Observatory in the late 90s and early 2000s. We will spend a year and a half mapping Bennu and have to wait until mid 2020 [when] we collect the sample, but it is pretty amazing to actually see it now. Christmas came early." The Arecibo work began shortly after the asteroid's discovery in 1999, when both the Puerto Rico...

Voyager 2 Makes It Through

by Paul Gilster | Dec 11, 2018 | Missions | 13 Comments

Voyager 2 has now gone interstellar, making it not only NASA's single longest-running mission but one of only two spacecraft that have crossed over from the heliosphere to true interstellar space, what scientists call the Local Interstellar Medium (LISM). On that note, it's interesting to put the Solar System in context. Depending on how you define the term, the Solar System takes in a great deal of interstellar space. Many astronomers put its outer edge at the outer Oort Cloud, perhaps 100,000 AU away, and both Voyagers have yet to reach the inner Oort. At an estimated 1,000 AU, the inner boundary of the Oort Cloud is where the vast cometary cloud around our star becomes apparent, housing in its entirety trillions of comets and extending about 40 percent of the way to the Alpha Centauri stars. The Voyagers will keep going, of course, and will reach the inner Oort in perhaps 300 years, though without working instrumentation. The steady diminishment of power from the crafts'...

The When and Where of Asteroid 101955 Bennu

by Paul Gilster | Dec 10, 2018 | Asteroid and Comet Deflection | 15 Comments

You wouldn't think the Yarkovsky effect would have any real significance on a half-kilometer wide pile of rubble like the asteroid 101955 Bennu. With a currently estimated mass somewhere between 60 and 80 billion kilograms, Bennu seems unlikely to receive much of a nudge from differences in heat on the object's surface. But the people who specialize in these things say otherwise. Sunlight warms one side of the asteroid while the other experiences the cold of space. Rotation keeps the dark side radiating heat, accounting for a tiny thrust. We call it the Yarkovsky effect after Ivan Osipovich Yarkovsky, a Polish engineer who came up with it in 1901, though if we want to give credit across the board, we might refer to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. Here we honor, in addition to Yarkovsky, an American scientist, a Russian astronomer and a NASA aerospace engineer, all of whom played a role in our understanding of the phenomenon as it relates to asteroids. Image:...

Exoplanet Possibilities in 12 Protoplanetary Disks

by Paul Gilster | Dec 7, 2018 | Exoplanetary Science | 1 Comment

Almost all the exoplanets we know have been detected in evolved stellar systems, places where the protoplanetary disk has dissipated and the planets around the star can be observed. Seeing inside a disk in formation is tricky business, though prominent studies at stars like Beta Pictoris have told us much about the evolution of these disks as planets do begin to emerge. But just how common are disks with ring and gap structures? Do all such disks produce planets? We're beginning to learn more as instruments like the Atacama Large Millimeter Array (ALMA) continue to be used to examine infant systems. Many of these show disks that are uniform in appearance, lacking discernible features like rings or gaps. Others are brighter, marked by concentric rings with separations that imply planet formation. It’s natural enough that early efforts have been devoted to brighter disks with their suggestion of planetary activity. Image: Until recently, protoplanetary disks were believed to be smooth,...

Helium Detection at HAT-P-11b

by Paul Gilster | Dec 6, 2018 | Exoplanetary Science | 9 Comments

You would think that helium, being the second most common element in the universe, would have been detected in exoplanet atmospheres long ago. A major constituent of the atmosphere at both Jupiter and Saturn, helium seems a natural because planets form from dust and gas from previous stellar generations, but it turns out that the first helium detection on an exoplanet occurred only this year, in a study led by Jessica Spake (University of Exeter). The planet in question, WASP-107b, yielded its helium signature in data gathered by the Hubble Space Telescope, a detection that showed clear signs of a comet-like tail forming as the planet's atmosphere escaped. Note the space-based detection: It's significant because Earth's atmosphere is opaque to the ultraviolet light the atoms in such an eroding atmosphere absorb. Could we make this kind of fine-grained study from the surface of the Earth? It turns out there's a way: Helium in its long-lived metastable state (as compared to its ground...

A Quick Riff on New Horizons

by Paul Gilster | Dec 5, 2018 | Outer Solar System | 16 Comments

We're starting to get a better view of Ultima Thule, the next destination for the New Horizons spacecraft, which is due to make its flyby of the Kuiper Belt Object also known as 2014 MU69 on New Year's Eve (0533 UTC January 1) The images below can't help but recall the gradual approach to Pluto/Charon as New Horizons closed on what turned out to be a spectacularly successful encounter. Here's hoping Ultima Thule is just as productive in teaching us something about Kuiper Belt Objects in general. Here's hoping, too, for another KBO flyby down the road. What we see in the dual images is the view (at the left) through LORRI (Long Range Reconnaissance Imager), averaging 10 individual 30-second exposures, with Ultima Thule just barely visible in the yellow circle. The component exposures were taken about a day before a course correction maneuver on December 2 and show Ultima visible against background stars. At the right is the image re-processed to remove the background starfield....

OSIRIS-REx: Arrival

by Paul Gilster | Dec 4, 2018 | Asteroid and Comet Deflection | 49 Comments

December 3 goes down as the day when OSIRIS-REx arrived at the asteroid called Bennu. The spacecraft, whose acronym untangles as Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, has been performing braking maneuvers to slow for the approach since October. This has been a long and delicate operation, with arrival marked by a maneuver on Monday to set up the first flyover of the object's north pole. Even so, spacecraft and asteroid are flying together while not yet in an orbital relationship. That won't happen until December 31, when the mission's navigation team will use the preliminary survey they're building now to initiate the orbit. Bear in mind that we are dealing with an object less than 500 meters across (about 1,600 feet), so one of Bennu's distinctions will be that it is to become the smallest object ever orbited by a spacecraft. Now the learning period intensifies. "During our approach toward Bennu, we have taken observations at much...

Slowing Star Formation: A Key to Astrobiology?

by Paul Gilster | Dec 3, 2018 | Deep Sky Astronomy & Telescopes | 2 Comments

The rate of star formation in our galaxy is about two new stars per year, a sedate pace that may play its role in the emergence of life. A new study out of Australian National University looks at the factors that can slow star formation, particularly in galaxies and star clusters still young enough to contain large amounts of dusty gas. What ANU's Roland Crocker and colleagues want to determine is an upper limit on how quickly stars can form in any giant gas cloud. It's an issue because conditions inside a tightly bound cluster could be inimical to life. Consider RMC 136, a concentration of stars at the heart of the Tarantula Nebula in the Large Magellanic Cloud. Here we have a cluster with an estimated mass of 450,000 solar masses, with a central concentration about 2 parsecs across. Star formation in this tightly crowded part of the cluster NGC 2070 is intense, but the tight quarters might turn out to be a serious issue. "If star formation happened rapidly, all stars would be bound...

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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