by Paul Gilster | Nov 23, 2020 | Culture and Society |
I’m tracking an online petition conceived by Jorge Santiago Ortiz that challenges the National Science Foundation: Repair the Arecibo Observatory, do not decommission it. Given Friday’s news of the planned shutdown due to problems with support cables and the dangers of possible repairs, it’s good to see an effort being made to explore the possible. Ortiz points out that the observatory employs more than 120 people, is visited by some 200 scientists every year working on research projects, and draws 100,000 visitors yearly from the general population.
I notice the petition is approaching 6,000 signatures this morning as people react to the Arecibo news. It is possible there is a path toward keeping the observatory alive? Also noted by Centauri Dreams reader Jeff Brandt, himself a resident of Puerto Rico, is an attempt to free the facility from National Science Foundation funding and repair the structure.
Brandt notes that Jenniffer González-Colón, Puerto Rico’s representative in the US Congress, has sent a letter to the House & Senate Appropriations Committee requesting funding to stabilize the structure, as you can see below. We’ll keep an eye on both efforts.
It seems apropos in discussing Arecibo to give a nod to the Cornell connection, given the university’s involvement in its inception and subsequent management. The radio telescope was conceived by Cornell professor William E. Gordon, while its early scientific investigations were coordinated by Thomas Gold, who created the Cornell Center for Radiophysics and Space Research. Looking back, the university’s Jonathan Lunine comments on its significance:
“Arecibo has been an incredibly productive facility for nearly 60 years. For the Cornell scientists and engineers who took a daring dream and realized it, for the scientists who made new discoveries with this uniquely powerful radio telescope and planetary radar, and for all the young people who were inspired to become scientists by the sight of this enormous telescope in the middle of the island of Puerto Rico, Arecibo’s end is an inestimable loss.”
Thoughts Upon Hearing the Arecibo Radio Observatory was About to be Closed
Which brings me to Henry Cordova, who has graced these pages before with his SETI Reality Check, and who now looks back at a visit to Arecibo in the observatory’s early days in an essay that was written, I hasten to add, before the recent news of the site’s decommissioning. Trained as an astronomer and mathematician, Henry’s interest in the ways in which we observe the stars continues unabated. Arecibo clearly called out the poetry in him, as it did in me.
by Henry Cordova
I visited Arecibo Observatory in 1971, I was in Puerto Rico on business, and I took a Sunday off to visit the place. It’s a two hour drive from San Juan, and nestled in some pretty spectacular jungle-covered Karst topography: a very beautiful drive into an isolated and haunted countryside.
When I arrived the place was deserted. There was a small building, similar to a motel, where I supposed visiting researchers were quartered; but nobody was home. The permanent staff probably had houses in town (Arecibo proper is about a half-hour drive further north, on the coast). Next door, the control room was visible; through the locked glass doors I could see electronic equipment, powered up, but no one was there. Only my car was in the parking area. At the edge of the lot was a little observation platform where you could walk right up to the edge of the dish itself. It spread before me, filling a vast natural depression. The feeling was very much like standing at the edge of Meteor Crater in Arizona, except I could see suspended above me, on huge white towers, the receivers placed at the focus of the parabola.
The silence, the isolation, the grandeur of it all really affected me. The sheer audacity of the structure, the combination of natural beauty and technological brilliance was almost overpowering. I imagine it would be very similar to be standing alone at Stonehenge on a sunny windy day, accompanied only by ghosts.
Observatories are holy places. They are as impressive and beautiful as a medieval cathedral and by necessity are usually located in lonely and desolate landscapes. Like cathedrals, they are temples to the ineffable, to the incredibly remote, and to our faith in being able to connect with it–places of worship, in a way, sacred places. I know it’s sentimental and impractical of me, but if this site is to be abandoned, let it not be replaced with a farm or village or reservoir or some other practical symbol of the economy. Let it naturally decay into ruins, as a monument to our boldness, and to our stupidity. Centuries from now, men will stand in that place and say ‘we once explored the stars from here’.
by Paul Gilster | Nov 20, 2020 | Culture and Society |
I always wanted to get to Arecibo, the magnificent 305-meter telescope that has for so long been a locus for radio astronomy research, but I was never able to make it to Puerto Rico. Now I’ve run out of time. The National Science Foundation doesn’t make these decisions lightly but multiple engineering companies have delivered assessments that point to catastrophic failure of the telescope structure as a real possibility. Too dangerous to repair, and faced with stability issues even if it could be repaired, the Arecibo Observatory will be decommissioned.
The breakdown in the vast structure has been ongoing, bits and pieces of news that added further dismay to an already dismal 2020. A support cable detached in August, resulting in an evaluation from the University of Central Florida, which manages the site. Replacement auxiliary cables were then on the way, temporary cables available, but on November 6 another main cable broke. The stresses on the second cable evidently told the story, making it clear that to proceed with repair would be to push against acceptable standards of safety.
Ralph Gaume, director of NSF’s Division of Astronomical Sciences, sums up the situation:
“Leadership at Arecibo Observatory and UCF did a commendable job addressing this situation, acting quickly and pursuing every possible option to save this incredible instrument. Until these assessments came in, our question was not if the observatory should be repaired but how. But in the end, a preponderance of data showed that we simply could not do this safely. And that is a line we cannot cross.”
Image: Arecibo Observatory’s 305-meter telescope in November of 2020. Credit: University of Central Florida.
It’s going to take some time for me to get my head around losing Arecibo, which has been since the early 1960s a part of my mental landscape when contemplating our civilization and its context in the cosmos. I had gotten to thinking in terms of ‘Arecibos’ of transmitting power, meaning that a dish like Arecibo could pick up an installation of comparable power over a span of 1,000 light years, a volume in which there are more than 10,000,000 stars. Ideas like that fueled my interest in SETI, which grew into a general passion for exoplanet research.
Remember, although we sometimes hear 51 Pegasi b referred to as the first exoplanet discovered, the honor actually belongs to the planets at the pulsar PSR B1257+12, which were found three years earlier in 1992 by Aleksander Wolszczan and Dale Frail using Arecibo data (51 Pegasi b was the first exoplanet found around a main sequence star, a valid distinction since pulsar planets are an unusual extreme as we contemplate the conditions extant in planetary systems). Speaking of pulsars, the first binary one was uncovered in Arecibo data in 1974 by Russell Hulse and Joseph H. Taylor, Jr., a find that earned the duo the Nobel Prize for Physics in 1993.
Arecibo has produced radar maps of Venus and Mercury and has charted near-Earth asteroids. As far back as 1965, it uncovered the actual rotation rate of Mercury (59 days as opposed to the previously believed 88). It analyzed the pulsar from the Crab Nebula supernova remnant in 1968 and performed the first radar ranging to an Earth-crossing asteroid (1862 Apollo) in 1980. Its planetary radar found evidence for hydrocarbon lakes on Titan and the observatory was used to study frequencies in the 1,000 MHz to 3,000 MHz range as part of the SETI effort.
Indeed, the list of accomplishments is far too long to list here, so I’ll direct you to this summary page. I do want to mention in the SETI context (although it was a matter of transmitting rather than listening) the 1974 message sent toward the globular cluster M13 by Frank Drake, primarily performed, I’m told, as a way of demonstrating what newly installed equipment could do. Even so, that transmission is an oft-cited marker in our thinking about our own place in the universe and the possibility of other technological civilizations we might encounter.
Invariably I think of Jill Tarter in terms of SETI, in this context because of her involvement in Project Phoenix, which moved to Arecibo in 1998 after stints at Parkes (Australia) and Green Bank (WV). As soon as I learned of Arecibo’s decommissioning, I wrote to ask for a comment. My own reflections on Arecibo hardly match the poetic depth of Dr. Tarter’s response:
I’ve been going to Arecibo since 1978. Over the decades, we’ve built a lot of Arecibo-specific hardware, written a lot of software, and bent the telescope control system into modes it was never designed for.
Arecibo was an impressive feat of engineering, a scientific workhorse, and it never lost that aura of being slightly exotic, no matter how many times I visited there; the constant croaking of the coquis [a frog common to Puerto Rico], the perfumes of the tropical forest, the local Ron del Barrelito [a rum said to be the best on the island], the Gregorian dome with its unmistakable compressor cadence, the jogging track underneath the dish ringed with small orchids, Orion rising over the treetops as seen from the balcony of the VSQ [Visiting Scientists Quarters], before heading off to my midnight shift of Project Phoenix observations, and the absolutely best view on the island from atop the platform.
But most of all I remember the staff and the resident scientists who were very close knit, offered us superb technical support, and threw wonderful parties with lots of dancing. It is very sad to witness the passing of this scientific Queen. She withstood powerful hurricanes, but age appears to have gotten the upper hand.
Arecibo’s demise also led me to touch base with Greg Matloff (New York City College of Technology (NYCCT)), whose work on interstellar propulsion was what originally drew me to the field (his Starflight Handbook, written with Eugene Mallove, was a frequently consulted text and provoked the research that led to my Centauri Dreams book in 2004). We had discussed Arecibo’s role in planetary protection in many conversations. Said Matloff:
“The loss of Arecibo is heartbreaking. This observatory has contributed so much to the study of Earth’s upper atmosphere, Solar System and deep sky objects, and SETI. But its greatest significance today is its service as planetary radar. Much of what we know about Near Earth Asteroids that might someday impact the Earth is due to the imaging capabilities of this instrument. It is my hope that an upgraded Arecibo can be constructed at the same site to continue this work of Earth Defense.”
That’s a hope many of us share, and we will see what comes of it. I do notice in the National Science Foundation’s materials on the decommissioning that NSF intends “to restore operations at assets such as the Arecibo Observatory LIDAR facility — a valuable geospace research tool — as well as at the visitor center and offsite Culebra facility, which analyzes cloud cover and precipitation data. NSF would also seek to explore possibilities for expanding the educational capacities of the learning center.”
What may emerge following telescope decommissioning is worth pondering.
by Paul Gilster | Nov 19, 2020 | Asteroid and Comet Deflection |
With successful operations at Ryugu (Hayabusa2) and Bennu (OSIRIS-REx), asteroid exploration seems to be moving full tilt, with the prospect of surface samples on the way. We can also look ahead to 16 Psyche, the object of interest for a NASA mission planned to launch in 2022, and the Lucy mission to Jupiter’s trojan asteroids, with launch now scheduled for 2021. The latest asteroid entry comes in the form of an interesting collaboration between the Japan Aerospace Exploration Agency (JAXA) and the German Aerospace Center (DLR) targeting asteroid 3200 Phaethon, a flyby mission designed to launch no earlier than 2024.
DESTINY+ is its name, the acronym standing for Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science (try to say all that quickly before you’ve had your morning coffee). The agreement for the bilateral mission was signed on November 11 as part of a joint strategy dialogue between the two space agencies.
The new mission continues German and Japanese cooperation in space. You may recall that DLR and the French space agency CNES (National Center for Space Studies) developed the MASCOT rover that was deployed on Ryugu in 2018, with several papers already published on its findings. The BepiColombo mission to Mercury grows out of ESA and Japanese collaboration, while the proposed Martian Moons eXploration (MMX) mission, developed by JAXA, will include a rover developed by DLR and CNES, along with scientific instrumentation from NASA.
At Phaethon, we’re looking at an interesting object, an Apollo asteroid that appears to be the parent body of the Geminids meteor shower. The Apollo asteroids are the largest group of near-Earth objects, numbering over 10,000, but among them, Phaethon has a special claim to fame. Carsten Henselowsky is DESTINY+ project manager at DLR:
“With a minimum approach distance of approximately 21 million kilometres, Phaethon gets closer to the Sun than the planet Mercury. In the process, its surface heats up to a temperature of over 700 degrees Celsius, causing the celestial body to release more dust particles. The aim of the DESTINY+ mission is to investigate such cosmic dust particles and to determine whether the arrival of extraterrestrial dust particles on Earth may have played a role in the creation of life on our planet.”
Image: Animation of Phaethon’s orbit. Credit: Phoenix7777. Data source: JPL HORIZONS. CC BY-SA 4.0.
The flyby will take the spacecraft to within 500 kilometers of Phaethon at a time in its orbit when the asteroid is approximately 150 million kilometers from the Sun. Key to the success of the mission is the DDA dust analyzer built by DLR (DESTINY+ Dust Analyzer). The plan is to study the dust environment through the entire four-year cruise to Phaethon, with projected flyby in 2028. The DDA is, according to this recent presentation at the Europlanet Science Congress, “the technological successor to the Cosmic Dust Analyzer (CDA) aboard Cassini-Huygens, which prominently investigated the dust environment of the Saturnian system.”
With the goal of determining the origin of each dust particle, mission scientists will be focusing on the proportion of organic matter given the possible delivery of organics to the early Earth by such particles. The asteroid is on a highly eccentric orbit resembling that of a comet more than an asteroid, crossing the orbits of Mercury, Venus, Earth and Mars. Dust tails have been observed coming from the object, likely the result of solar heat creating surface fractures.
Launch will be aboard an Epsilon S vehicle from the Uchinoura Space Center in Japan. The spacecraft will use solar-electric propulsion, with a 1.5-year period after launch in which it will raise its orbit. A series of lunar flybys will then accelerate the probe into an interplanetary trajectory. The scientific payload will, in addition to the dust analyzer, include two cameras: The Telescopic Camera for Phaethon (TCAP) and the Multi-band Camera for Phaethon, MCAP.
By chance, I ran across a passage this morning in Oliver Morton’s book The Moon: A History for the Future (The Economist, 2019) that explains why it takes so long to get to objects that, like NEAs, sound as though they should be nearby. Such serendipity coaxes me into quoting it:
…what matters in space is delta-v, not distance. To get from the Moon to the Earth requires only about a fifth of the delta-v that is needed to make the same journey in the opposite direction. Another demonstration of this proposition is that the amount of delta-v it takes to get a spacecraft to the surface of the Moon can also get it to destinations much farther afield. “Near-Earth asteroids” (NEA) are only near inasmuch as they have orbits that very occasionally bring them moderately close to the Earth. At any given time a typical NEA will be 100 or 200 times as far away as the Moon. But in terms of delta-v, quite a lot of these asteroids are just as easy to reach as the Moon is; it is just a matter of getting on to the right trajectory and waiting. Indeed, it takes no more delta-v to reach the little moons of Mars than it does the great Moon of Earth (the surface of Mars is another matter).
Image: Asteroid explorer DESTINY+. Credit: JAXA/Kashikagaku.
by Paul Gilster | Nov 18, 2020 | Exoplanetary Science |
How is a planet’s composition related to its host star? The European Space Agency’s ARIEL mission (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is designed to probe the question, examining planetary atmospheres to determine the composition, temperature and chemical processes at work in a large sample of planetary systems.
Transmission spectroscopy is the method, examining spectra as known exoplanets pass in front of, then behind their host stars. Researchers will use light filtering through the atmospheres to unlock the chemical processes within each. ARIEL will survey about 1,000 planetary systems in both visible and infrared wavelengths, probing not just chemistry but the thermal conditions that affect their composition. The mission’s focus is on super-Earths to gas giants, all with temperatures greater than 320 Celsius.
I suspect that principal investigator Giovanna Tinetti (University College London) has been asked about the choice of targets to the point of exhaustion, but one reason for focusing on planets in this size and temperature range is our need to build up a catalog of atmospheres that will inform the entire field, so that when we drill down to small, rocky worlds using future instruments, we’ll have a context in which to place what we see. A high temperature atmosphere is helpful here because it remains in continuous circulation, without the obscuring clouds that make characterization difficult.
Image: Giovanna Tinetti (University College London), principal investigator for ARIEL.
ARIEL will be positioned around L2, the second Sun-Earth Lagrange point, 1.5 million kilometres directly ‘behind’ Earth as viewed from the Sun. A just released ESA report explains the issues the mission will investigate, noting the wide range of planets and stars:
This large and unbiased survey will contribute to answering the first of the four ambitious topics listed in the ESA’s Cosmic Vision: “What are the conditions for planet formation and the emergence of life?”. Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. There is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet’s surface and atmosphere is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth and evolution.
Remember, too, the statistical nature of the inquiry. The sample population is large, so that we move from the small number of atmospheres currently characterized to hundreds. Our understanding of the early stages of planet and atmosphere formation during the first few million years in an infant system as it emerges from the nebular phase should help us relate the chemistry in exoplanets to their other parameters and to the chemical environment of the star.
Image: An example spectrum Ariel could measure from light passing through an exoplanet’s atmosphere. Credit: ESA/STFC RAL Space/UCL/UK Space Agency/ATG Medialab.
Key components — water vapor, carbon dioxide, methane — of planetary atmospheres will be detected, but also more unusual metallic compounds that define the chemical environment within each system studied. For a smaller number of target planets, the spacecraft will perform a survey of cloud systems and atmospheric changes at a seasonal and daily level. Says ARIEL project scientist Theresa Lueftinger: “Our chemical census of hundreds of solar systems will help us understand each planet in context of the chemical environment and composition of the host star, in turn helping us to better understand our own cosmic neighbourhood.”
ESA has just announced that ARIEL has moved from study to implementation phase, the step before negotiations begin with industrial contractors to build the spacecraft, which is scheduled for launch from Kourou (French Guiana) in 2029. Bids on spacecraft hardware will be requested within months, with the prime contractor chosen by the summer of 2021. 50 institutes from 17 European countries are involved, as is NASA, in the payload module, which will have at its heart a one-meter class cryogenic telescope along with associated science instruments.
Three ESA missions with an exoplanet charter are thus framed within a ten-year window, with ARIEL joined by CHEOPS (CHaracterising ExOPlanet Satellite), launched in December 2019, and PLATO (PLAnetary Transits and Oscillations of stars), to be launched in 2026. The latter emphasizes rocky planets in the habitable zone of Sun-like stars.
To keep up with ARIEL, you may want to follow @ArielTelescope on Twitter. You’ll find background information in the recently published ARIEL Definition Study Report, available here.
by Paul Gilster | Nov 17, 2020 | Outer Solar System |
How salty should we expect the ice on Europa’s surface to be? It would be helpful to know, because the salinity of the surface will be a factor in how transparent the ice shell is to radar waves. Europa Clipper will fly with an instrument called REASON — Radar for Europa Assessment and Sounding: Ocean to Near-surface — which will be investigating both the surface ice and the ocean beneath. Recent research, in which its principal investigator, Don Blankenship (University of Texas), is involved is offering insights into the salinity of the ice.
Here’s a bit of background on REASON from a NASA page on Europa Clipper:
Depending on their wavelength, radio waves can either bounce off or penetrate different materials. REASON will use high frequency (HF) and very high frequency (VHF) radio signals to penetrate up to 18 miles (30 kilometers) into Europa’s ice to look for the moon’s suspected ocean, measure ice thickness, and better understand the icy shell’s structure. The instrument will also study the elevation, composition, and roughness of Europa’s surface, and will search Europa’s upper atmosphere for signs of plume activity.
Image: Europa Clipper, scheduled for launch in 2024. Credit: NASA/JPL-Caltech.
So plumes are in play for Europa Clipper, and the new research finds evidence of a process that can produce them. The paper in Geophysical Research Letters focuses on what the authors call brine migration, in which small pockets of salty water migrate within the ice to warmer icy areas. We get into questions of salinity in this work because migration of icy brines, analyzed here through study of the impact crater Manannán, may have resulted in the creation of a plume. Imaging data from the Galileo mission allowed the team to study the resulting surface feature and to calculate that Europa’s ocean is about a fifth as salty as Earth’s.
But let’s back up to that plume. If eruptions from the ocean below periodically break through the ice, we might have a way to sample ocean materials without ever trying to drill through the surface shell. The new work, led by Gregor Steinbrügge (Stanford University) homes in on Manannán, a 30-kilometer wide crater on Europa that is the result of an impact some tens of millions of years ago. The paper models the melting and refreezing of water following the event. And it suggests that not all plumes carry materials from the ocean below.
Manannán is located on Europa’s trailing hemisphere at 3°0’N and 120°50’E. The crater was imaged by the Galileo spacecraft’s Near-Infrared Mapping Spectrometer. Subsequent geological mapping of Manannán has shown what appear to be impact melt materials filling the crater floor, along with ejecta deposits that would have been brought up from below at the time of impact.
According to the researchers, as water transformed back into ice following the impact, pockets of water with higher salt content were created in the surface, migrating sideways through the shell by melting adjacent areas of less salty ice. “We developed a way that a water pocket can move laterally – and that’s very important,” says Steinbru?gge. “It can move along thermal gradients, from cold to warm, and not only in the down direction as pulled by gravity.”
Image: This illustration of Jupiter’s icy moon Europa depicts a cryovolcanic eruption in which brine from within the icy shell could blast into space. A new model proposing this process may also shed light on plumes on other icy bodies. Credit: Justice Wainwright.
Pockets of brine moving about within the surface become saltier as they move through less salty water around them and eventually erupt, according to this model, which shows freezing and pressurization as the factors leading to a cryovolcanic event. At Manannán crater, a migrating brine pocket finally freezing at the center generated a plume estimated to be 1-2 kilometers high, leaving a surface feature, roughly spider-like in shape, that turned up in the Galileo data. The spider-shaped fractures consist of 17 segments, surrounded by a series of concentric faults. This would have been a relatively small plume, and the Manannán findings do not explain what may be larger plumes hypothesized based on Hubble and Galileo data.
Image: The ‘spider’ feature within Manannán impact crater. Credit: NASA.
The point is that brine pocket migration is a surface phenomenon that can generate plumes, implying that such plumes do not require a connection with the ocean beneath. Whether there are other, larger plumes that do make such connections has not yet been determined.
Oceanic origin or not, all of this makes Europa’s surface an even more dynamic place than we’ve been considering, while somewhat tempering our expectations for astrobiology in plume activity even as we continue to observe the moon for future, perhaps much larger plumes. The team’s modeling of how melting and subsequent freezing of a water pocket within the icy shell would produce an eruption should have implications for other icy bodies within the Solar System. Robert Pappalardo (JPL) is a project scientist on the Europa Clipper mission:
“The work is exciting, because it supports the growing body of research showing there could be multiple kinds of plumes on Europa. Understanding plumes and their possible sources strongly contributes to Europa Clipper’s goal to investigate Europa’s habitability.”
The paper is Steinbru?gge et al. ,”Brine Migration and Impact?Induced Cryovolcanism on Europa,” Geophysical Research Letters 5 November 2020 (abstract).
