Eugene Parker Solar Probe

NASA Renames Solar Probe Mission to Honor Pioneering Physicist Eugene Parker

NASA has renamed the Solar Probe Plus spacecraft — humanity’s first mission to a star, which will launch in 2018 — as the Parker Solar Probe in honor of astrophysicist Eugene Parker. The announcement was made at a ceremony at the University of Chicago, where Parker serves as the S. Chandrasekhar Distinguished Service Professor Emeritus, Department of Astronomy and Astrophysics.

In 1958, Parker — then a young professor at the university’s Enrico Fermi Institute — published an article in the Astrophysical Journal called “Dynamics of the interplanetary gas and magnetic fields.” Parker believed there was high speed matter and magnetism constantly escaping the sun, and that it affected the planets and space throughout our solar system.

This phenomenon, now known as the solar wind, has been proven to exist repeatedly through direct observation. Parker’s work forms the basis for much of our understanding about how stars interact with the worlds that orbit them.

In the 1950s, Parker proposed a number of concepts about how stars — including our sun — give off energy. He called this cascade of energy the solar wind, and he described an entire complex system of plasmas, magnetic fields and energetic particles that make up this phenomenon. Parker also theorized an explanation for the superheated solar atmosphere, the corona, which is — contrary to what was expected by physics laws — hotter than the surface of the sun itself. Many NASA missions have continued to focus on this complex space environment defined by our star — a field of research known as heliophysics.

“Parker Solar Probe is going to answer questions about solar physics that we’ve puzzled over for more than six decades,” said Parker Solar Probe Project Scientist Nicola Fox, of the Johns Hopkins University Applied Physics Laboratory. “It’s a spacecraft loaded with technological breakthroughs that will solve many of the largest mysteries about our star, including finding out why the sun’s corona is so much hotter than its surface. And we’re very proud to be able to carry Gene’s name with us on this amazing voyage of discovery.”

Born on June 10, 1927, in Michigan, Eugene Newman Parker received a Bachelor of Science in physics from Michigan State University and a doctorate from Caltech. He then taught at the University of Utah, and since 1955, Parker has held faculty positions at the University of Chicago and at its Fermi Institute. He has received numerous awards for his research, including the George Ellery Hale Prize, the National Medal of Science, the Bruce Medal, the Gold Medal of the Royal Astronomical Society, the Kyoto Prize, and the James Clerk Maxwell Prize.

Parker Solar Probe is on track for launch during a 20-day window that opens July 31, 2018. The mission is part of NASA’s Living With a Star program to explore aspects of the sun-Earth system that directly affect life and society. LWS is managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland, for NASA’s Science Mission Directorate in Washington, D.C. Johns Hopkins APL manages the mission for NASA and is designing and building and will operate the spacecraft.

By Geoff Brown
Johns Hopkins University Applied Physics Laboratory

 

Habitable Moist Atmospheres

Habitable Moist Atmospheres On Terrestrial Planets Near the Inner Edge Of the Habitable Zone Around M-dwarfs

ABSTRACT: Terrestrial planets in the habitable zones (HZs) of low-mass stars and cool dwarfs have received significant scrutiny recently because their shorter orbital periods increase their chances of detection and characterization compared to planets around G-dwarfs. As these planets are likely tidal-locked, improved 3D numerical simulations of such planetary atmospheres are needed to guide target selection. Here we use a 3-D climate system model, updated with new water-vapor absorption coefficients derived from the HITRAN 2012 database, to study ocean covered planets at the inner edge of the HZ around late-M to mid-K stars (2600K <= Teff <= 4500K). Our results indicate that these updated water-vapor coefficients result in significant warming compared to previous studies, so the inner HZ around M-dwarfs is not as close as suggested by earlier work. Assuming synchronously rotating planets, we find that planets at the inner HZ of stars with Teff > 3000K undergo the classical “moist-greenhouse” (H2O mixing ratio > 10-3 in the stratosphere) at significantly lower surface temperature (~ 280K) in our 3-D model compared with 1-D climate models (~ 340K). This implies that some planets around low mass stars can simultaneously undergo water-loss and remain habitable. However, for star with Teff <= 3000K, planets at the inner HZ may directly transition to a runaway state, while bypassing the moist greenhouse water-loss entirely. We analyze transmission spectra of planets in a moist green- house regime, and find that there are several prominent H2O features, including a broad feature between 5-8 microns, within JWST MIRI instrument range. Thus, relying only upon standard Earth-analog spectra with 24-hour rotation period around M-dwarfs for habitability studies will miss the strong H2O features that one would expect to see on synchronously rotating planets around M-dwarf stars, with JWST.

 

The Spin States of Exoplanets

On the Spin States of Habitable Zone Exoplanets Around M Dwarfs: The Effect of a Near-Resonant Companion

ABSTRACT: One longstanding problem for the potential habitability of planets within M dwarf systems is their likelihood to be tidally locked in a synchronously rotating spin state. This problem thus far has largely been addressed only by considering two objects: the star and the planet itself. However, many systems have been found to harbor multiple planets, with some in or very near to mean-motion resonances. The presence of a planetary companion near a mean-motion resonance can induce oscillatory variations in the mean-motion of the planet, which we demonstrate can have significant effects on the spin-state of an otherwise synchronously rotating planet. In particular, we find that a planetary companion near a mean-motion resonance can excite the spin states of planets in the habitable zone of small, cool stars, pushing otherwise synchronously rotating planets into higher amplitude librations of the spin state, or even complete circulation resulting in effective stellar days with full surface coverage on the order of years or decades. This increase in illuminated area can have potentially dramatic influences on climate, and thus on habitability. We also find that the resultant spin state can be very sensitive to initial conditions due to the chaotic nature of the spin state at early times within certain regimes. We apply our model to two hypothetical planetary systems inspired by the K00255 and TRAPPIST-1 systems, which both have Earth-sized planets in mean-motion resonances orbiting cool stars.

 

KIC 8462852: Will the Trojans return

KIC 8462852: Will the Trojans return in 2021?

ABSTRACT: KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide and asymmetric dimming taking up to 15 per cent of the total light, together with a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Trojan objects sharing its orbit that causes the second period of multiple dimmings. The resulting orbital period is T≈12 years, with a semi-major axis a≈6 au. In this context the recent observation of a minor dimming can be explained as a secondary eclipse produced by the passage of the planet behind the star. Our model allows us to make two straightforward predictions: we expect the passage of a new swarm of Trojans in front of the star starting during the early months of 2021, and a new transit of the main object during the first half of 2023.

 

ALMA Eyes Icy Ring around Fomalhout

ALMA Eyes Icy Ring around Young Planetary System


Composite image of the Fomalhaut star system. The ALMA data, shown in orange, reveal the distant and eccentric debris disk in never-before-seen detail. The central dot is the unresolved emission from the star, which is about twice the mass of our sun.

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has made the first complete millimeter-wavelength image of the ring of dusty debris surrounding the young star Fomalhaut. This remarkably well-defined band of rubble and gas is likely the result of exocomets smashing together near the outer edges of a planetary system 25 light-years from Earth.

“ALMA has given us this staggeringly clear image of a fully formed debris disk,” said Meredith MacGregor, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author on one of two papers accepted for publication in the Astrophysical Journal describing these observations. “We can finally see the well-defined shape of the disk, which may tell us a great deal about the underlying planetary system responsible for its highly distinctive appearance.”

Fomalhaut is a relatively nearby star system and one of only about 20 in which planets have been imaged directly. The entire system is approximately 440 million years old, or about one-tenth the age of our solar system.

As revealed in the new ALMA image, a brilliant band of icy dust about 2 billion kilometers wide has formed approximately 20 billion kilometers from the star.

Debris disks are common features around young stars and represent a very dynamic and chaotic period in the history of a solar system. Astronomers believe they are formed by the ongoing collisions of comets and other planetesimals in the outer reaches of a recently formed planetary system. The leftover debris from these collisions absorbs light from its central star and reradiates that energy as a faint millimeter-wavelength glow that can be studied with ALMA.

Using the new ALMA data and detailed computer modeling, the researchers were able to calculate the precise location, width, and geometry of the disk. These parameters confirm that such a narrow ring is likely produced through the gravitational influence of planets in the system, noted MacGregor.

The new ALMA observations are also the first to definitively show “apocenter glow,” a phenomenon predicted in a 2016 paper by Margaret Pan, a scientist at the Massachusetts Institute of Technology in Cambridge, who is also a co-author on the new ALMA papers. Like all objects with elongated orbits, the dusty material in the Fomalhaut disk travels more slowly when it is farthest from the star. As the dust slows down, it piles up, forming denser concentrations in the more distant portions of the disk. These dense regions can be seen by ALMA as brighter millimeter-wavelength emission.

Using the same ALMA dataset, but focusing on distinct millimeter-wavelength signals naturally emitted by molecules in space, the researchers also detected vast stores of carbon monoxide gas in precisely the same location as the debris disk.

“These data allowed us to determine that the relative abundance of carbon monoxide plus carbon dioxide around Fomalhaut is about the same as found in comets in our own solar system,” said Luca Matrà with the University of Cambridge, UK, and lead author on the team’s second paper. “This chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own.” Matrà and his colleagues believe this gas is either released from continuous comet collisions or the result of a single, large impact between supercomets hundreds of times more massive than Hale-Bopp.

The presence of this well-defined debris disk around Fomalhaut, along with its curiously familiar chemistry, may indicate that this system is undergoing its own version of the Late Heavy Bombardment, a period approximately 4 billion years ago when the Earth and other planets were routinely struck by swarms of asteroids and comets left over from the formation of our solar system.

“Twenty years ago, the best millimeter-wavelength telescopes gave the first fuzzy maps of sand grains orbiting Fomalhaut. Now with ALMA’s full capabilities the entire ring of material has been imaged,” concluded Paul Kalas, an astronomer at the University of California at Berkeley and principal investigator on these observations. “One day we hope to detect the planets that influence the orbits of these grains.”

 

What’s Up with Tabby’s Star?

What’s Up with Tabby’s Star?

by Gerald Harp

By now you have surely heard that Boyajian’s star, aka Tabby’s star, aka KIC8462852, is going through another weird dimming phase. We do not have a satisfactory explanation for why Boyajian’s star sometimes dims by 20%, and many astronomers are monitoring the star with optical and infrared telescopes, hoping to learn more about this strange behavior. Likewise, the SETI Institute has shifted into gear using our own radio telescope, the Allen Telescope Array (ATA) to monitor Boyajian’s star for the presence of artificial radio transmissions that could reveal a civilization like ours in that system.

Backing up a bit, remember that Boyajian’s star was discovered in data from the Kepler space telescope and shows the most unusual “dimming” of a star ever observed.  From time to time, the light from this star is blocked by some enormous quantity of material moving between the star and our telescopes. But this material is unexpectedly cold and does not give off the infrared radiation expected if it were orbiting the star in a relatively close orbit. This mysterious material is too big and too cold to be explained by a typical orbiting planet, and some scientists have wondered if we could instead be observing a giant structure built by an advanced civilization. For example, a huge megastructure is just what you would need to capture an enormous quantity of stellar energy to power massive engineering projects. Even more interesting, the timing of the present dip suggests that whatever this material is, it is situated at just the right distance from the star to be in the “habitable zone,” where we believe that life like ours could develop as it has on Earth.

So, last Thursday, as soon as we heard Boyajian’s star began another dimming phase, the SETI Institute reacted quickly and pointed our ATA toward that star with hopes of catching a tell-tale signal that might reveal a technological civilization. Using the same methods as in our previous study of the star (http://iopscience.iop.org/article/10.3847/0004-637X/825/2/155), we are making very deep and careful observations for signals that appear to be artificial – signals that could be generated by no known natural process.

 

Jupiter’s magnetosphere

Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits

Abstract

The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.

The Juno Mission serves two principal science objectives. The first is to understand the origin and evolution of Jupiter, informing the formation of our solar system and planetary systems around other stars. Servicing this objective, Juno’s measurements of gravity, magnetic fields, and atmospheric composition and circulation probe deep inside Jupiter to constrain its interior structure and composition. The second objective takes advantage of Juno’s close-in polar orbits to explore Jupiter’s polar magnetosphere and intense aurorae. From a vantage point above the poles, Juno’s fields and particles instrumentation gather direct in situ observations of the particle populations exciting the aurora, which are imaged simultaneously by Juno’s ultraviolet (UV) and infrared (IR) imaging spectrographs.

Summary

Juno has provided observations of fields and particles in the polar magnetosphere of Jupiter, as well as high-resolution images of the auroras at UV and IR wavelengths. Although many of the observations have terrestrial analogs, it appears that different processes are at work in exciting the aurora and in communicating the ionosphere-magnetosphere interaction. We observed plasmas upwelling from the ionosphere, providing a mechanism whereby Jupiter helps populate its magnetosphere. The weakness of the magnetic field-aligned electric currents associated with the main aurora and the broadly distributed nature of electron beaming in the polar caps suggest a radically different conceptual model of Jupiter’s interaction with its space environment. The (precipitating) energetic particles associated with jovian aurora are very different from the peaked energy distributions that power the most intense auroral emissions at Earth.

 

Jupiter’s interior and deep atmosphere

Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft

Jupiter is the largest and most massive planet in our solar system. NASA’s Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno’s flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter’s aurorae and plasma environment, both as Juno approached the planet and during its first close orbit.

Science, this issue p. 821, p. 826

Abstract

On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno’s measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter’s core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.

The primary science goal of Juno is to improve our understanding of the origin and evolution of Jupiter, the history of the solar system, and planetary system formation in general. To constrain Jupiter’s interior structure, Juno’s onboard instruments probe below the cloud decks, gathering data about the planet’s gravity, magnetic fields, and deep atmospheric composition. Juno’s elliptical orbit provides multiple periapsis passes very close to Jupiter, within 1.06 Jupiter radii (RJ) of the jovigraphic equator, on its pole-to-pole trajectory. Measurements associated with a second science goal use Juno’s unprecedented close-in polar orbits to explore Jupiter’s polar magnetosphere and intense aurorae.

Juno’s suite of science instruments includes X-band and Ka-band communications subsystems for determining Jupiter’s gravity field, dual magnetometers to map Jupiter’s high-order internal magnetic field, a six-channel microwave radiometer (MWR) operating at wavelengths between 1 and 50 cm to probe Jupiter’s deep atmosphere, and a color camera (JunoCam) and an infrared spectrometer and imager (JIRAM) to capture views of Jupiter. Juno also carries a suite of field and particle instruments for in situ sampling of Jupiter’s magnetosphere and investigation of its powerful aurora.

Summary

The results from Juno’s initial close passes of Jupiter are changing our understanding of this gas giant. Juno’s direct glimpse of Jupiter’s poles shows numerous cyclonic storms clustered together and a storm illuminated in Jupiter’s nightside that provided a measurement of its vertical extent. The deep microwave sounding of Jupiter by Juno demonstrates the power of this technique for unveiling spatial and temporal structure in the ammonia abundance. The initial measurement of Jupiter’s gravity will inform interior models with implications for the extent, existence, and mass of Jupiter’s core. The magnitude of the observed magnetic field observed was 7.766 G, almost twice as strong as expected. More results from Juno’s initial passes are discussed in a companion paper.

 

No snowball on tidally locked planets

No snowball on habitable tidally locked planets

ABSTRACT: The TRAPPIST-1, Proxima Centauri, and LHS 1140 systems are the most exciting prospects for future follow-up observations of potentially inhabited planets. All orbit nearby M-stars and are likely tidally locked in 1:1 spin-orbit states, which motivates the consideration of the effects that tidal locking might have on planetary habitability. On Earth, periods of global glaciation (snowballs) may have been essential for habitability and remote signs of life (biosignatures) because they are correlated with increases in the complexity of life and in the atmospheric oxygen concentration. In this paper we investigate the snowball bifurcation (sudden onset of global glaciation) on tidally locked planets using both an energy balance model and an intermediate-complexity global climate model. We show that tidally locked planets are unlikely to exhibit a snowball bifurcation as a direct result of the spatial pattern of insolation they receive. Instead they will smoothly transition from partial to complete ice coverage and back. A major implication of this work is that tidally locked planets with an active carbon cycle should not be found in a snowball state. Moreover, this work implies that tidally locked planets near the outer edge of the habitable zone with low CO2 outgassing fluxes will equilibrate with a small unglaciated substellar region rather than cycling between warm and snowball states. More work is needed to determine how the lack of a snowball bifurcation might affect the development of life on a tidally locked planet.

 

KIC 8462852 dims again

Star that spurred alien megastructure theories dims again

By Daniel Clery|May. 22, 2017 , 5:30 PM

Astronomers and alien life enthusiasts alike are buzzing over the sudden dimming of an otherwise unremarkable star 1300 light-years away in the constellation Cygnus. KIC 8462852 or “Tabby’s star” has dimmed like this several times before, prompting some researchers to suggest that the megastructures of an advanced alien civilization might be blocking its light. And now—based on new data from numerous telescopes—it’s doing it again.

“This is the first clear dip we have seen since [2013], and the first we have ever caught in real time,” says Jason Wright, an astronomer at Pennsylvania State University in State College. If they can rope in more telescopes, astronomers hope to gather enough data to finally figure out what’s going on. “This could be the first of several dips about to come,” says astronomer David Kipping of Columbia University. “Many observers will be closely watching.”

KIC 8462852 was first noticed to be dipping in brightness at seemingly random intervals between 2011 and 2013 by NASA’s Kepler telescope. Kepler, launched to observe the stellar dimmings caused when an exoplanet passes in front of its star, revealed that the dimming of Tabby’s star was much more erratic than a typical planetary transit. It was also more extreme, with its brightness sometimes dropping by as much as 20%. This was not the passage of a small circular planet, but of something much larger and more irregular.

The team that made this discovery, led by Yale University astronomer Tabetha Boyajian—the star’s namesake—suggested a variety of explanations for its strange behavior, including that the star itself was variable, that it was surrounded by clouds of dust or dusty comets, or that planets around it had collided or were still forming. But KIC 8462852 hit the headlines when Wright and colleagues suggested that the star would be a good candidate to search for evidence of a large manufactured structure built by alien life.

Further studies didn’t find the infrared “glow” expected from a large object orbiting close to its star. But neither did they confirm—or refute—any other explanations. Astronomers needed to observe the star closely and take spectra—the distribution of light emitted at various wavelengths—during a dimming. For that they had to wait. Kepler stopped looking at the sky around Tabby’s star in 2013, so Boyajian and her team have been keeping an eye on KIC 8462852 with the help of a network of amateur star watchers and, more recently, with the privately run Las Cumbres Observatory, a network of 18 robotic telescopes at six sites around the world.

The first sign of the star’s recent dimming came on 24 April from Tennessee State University’s Fairborn Observatory in southern Arizona. But it wasn’t until late last week that astronomers were sure it had entered a new dip. It was 3% dimmer than its normal brightness on 19 and 20 May and is now moving back toward normal. “It looks like the dip has mostly ended,” Kipping says. “But … in the Kepler data we saw an episode of multiple dips clustered together over the span of a few weeks.” The progress of the dimming over the past few days also bears a passing resemblance to some detected by Kepler, supporting the idea that the same object is repeatedly passing in front of the star.

Observers are ready for further changes. “There’s been an enormously positive response from the community,” says Boyajian, now at Louisiana State University in Baton Rouge, with people interrupting ongoing projects to take observations of KIC 8462852. Astronomers from about a dozen different observatories managed to capture spectra from the star during the dimming. So, just what is happening around the star? Boyajian says that combining the different spectra into a coherent picture across the wavelengths may take a while. “A physical interpretation of what’s going on will take more work. But the process has begun.”