Experience in exploring our own solar system has shown that direct investigation of planetary bodies using space probes invariably yields scientific knowledge not otherwise obtainable. In the case of exoplanets, such direct investigation may be required to confirm inferences made by astronomical observations, especially with regard to planetary interiors, surface processes, geological evolution, and possible biology. This will necessitate transporting sophisticated scientific instruments across interstellar space, and some proposed methods for achieving this with flight-times measured in decades are reviewed. It is concluded that, with the possible exception of very lightweight (and thus scientifically limited) probes accelerated to velocities of ~0.1c with powerful Earth-based lasers, achieving such a capability may have to wait until the development of a space-based civilization capable of leveraging the material and energy resources of the solar system.
Monday, July 31, 2017
Friday, July 28, 2017
Not all stars are good parents to their budding planets — some get downright nasty and kick their children into interstellar space.We’ve found a handful of these free orphaned planets before, and they’re called “rogue planets.” But a study today in Nature Astronomy suggests that the type we’ve seen so far, which are all gas giant sized, are the exception, not the norm.“Basically, it is much easier to eject an Earth-mass planet than a Jupiter-mass planet,” Przemek Mróz, lead author of the paper and a PhD candidate at the University of Warsaw, says.
Thursday, July 27, 2017
Teachey et al
Exomoons represent an outstanding challenge in modern astronomy, with the potential to provide rich insights into planet formation theory and habitability. In this work, we stack the phase-folded transits of 284 viable moon hosting Kepler planetary candidates, in order to search for satellites. These planets range from Earth-to-Jupiter sized and from ~0.1 to 1.0 AU in separation - so-called "warm" planets. Our data processing includes two-pass harmonic detrending, transit timing variations, model selection and careful data quality vetting to produce a grand light curve with a r.m.s. of 5.1 ppm. We find that the occurrence rate of Galilean-analog moon systems can be constrained to be η less than 0.38 to 95% confidence for the 284 KOIs considered, with a 68.3% confidence interval of η=0.16+0.13−0.10. A single-moon model of variable size and separation locates a slight preference for a population of Super-Ios, ~0.5 R_Earth moons orbiting at 5-10 planetary radii. However, we stress that the low Bayes factor of just 2 in this region means it should be treated as no more than a hint at this time. Splitting our data into various physically-motivated subsets reveals no strong signal. The dearth of Galilean-analogs around warm planets places the first strong constraint on exomoon formation models to date. Finally, we report evidence for an exomoon candidate Kepler-1625b I, which we briefly describe ahead of scheduled observations of the target with the Hubble Space Telescope.
Wednesday, July 26, 2017
The EBLM Project IV. Spectroscopic orbits of over 100 eclipsing M dwarfs masquerading as transiting hot-Jupiters
Amaury et al
We present 2271 radial velocity measurements taken on 118 single-line binary stars, taken over eight years with the CORALIE spectrograph. The binaries consist of F/G/K primaries and M-dwarf secondaries. They were initially discovered photometrically by the WASP planet survey, as their shallow eclipses mimic a hot-Jupiter transit. The observations we present permit a precise characterisation of the binary orbital elements and mass function. With modelling of the primary star this mass function is converted to a mass of the secondary star. In the future, this spectroscopic work will be combined with precise photometric eclipses to draw an empirical mass/radius relation for the bottom of the mass sequence. This has applications in both stellar astrophysics and the growing number of exoplanet surveys around M-dwarfs. In particular, we have discovered 34 systems with a secondary mass below 0.2M⊙, and so we will ultimately double the known number of very low-mass stars with well characterised mass and radii.
We are able to detect eccentricities as small as 0.001 and orbital periods to sub-second precision. Our sample can revisit some earlier work on the tidal evolution of close binaries, extending it to low mass ratios. We find some binaries that are eccentric at orbital periods < 3 days, while our longest circular orbit has a period of 10.4 days.
By collating the EBLM binaries with published WASP planets and brown dwarfs, we derive a mass spectrum with twice the resolution of previous work. We compare the WASP/EBLM sample of tightly-bound orbits with work in the literature on more distant companions up to 10 AU. We note that the brown dwarf desert appears wider, as it carves into the planetary domain for our short-period orbits. This would mean that a significantly reduced abundance of planets begins at ∼3MJup, well before the Deuterium-burning limit.
Monday, July 24, 2017
The Pale Red Dot team is coasting off the success of their discovery last year of a planet in the Proxima Centauri system system by casting its net even wider as the Red Dots campaign.Whereas Pale Red Dot focused just on Proxima Centauri, Red Dots is looking toward Barnard’s Star and Ross 154 as well. These three stars will be held up to intense scrutiny by the team in the hunt for planets — or in the case of Proxima, additional planets.Barnard’s Star has been a popular target since the 1963 announcement by Swarthmore College professor Peter van de Kamp of a Jupiter-mass planet around it. His observations ended up discredited, as the telescope he used at Sproul Observatory had a flaw that caused some stars to appear to “wobble” when they were doing no such thing.“We are inviting anyone willing to collaborate to observe the stars’ brightnesses and to join our campaign,” Mikko Tuomi, a European Southern Observatory astronomer and Red Dots scientist, said in an email. “We have already 1,700 brightness observations of Ross 154 from five different observers and as many as 2,500 brightness observations of Barnard’s star from as many as nine observers (Barnard’s star is on the northern sky, so more accessible for US and European observers) using as many independent telescopes helping us in studying the variability of these stars in detail.”
Friday, July 21, 2017
One night three months ago, Rosa Castro finished her dinner, opened her laptop, and uncovered a novel object that was neither planet nor star. Therapist by day and amateur astronomer by night, Castro joined the NASA-funded Backyard Worlds: Planet 9 citizen science project when it began in February -- not knowing she would become one of four volunteers to help identify the project's first brown dwarf, formally known as WISEA J110125.95+540052.8.
Wednesday, July 19, 2017
Dark stars may not just be for Grateful Dead fans anymore.In a new paper uploaded to arXiv, Rutgers University astrophysics professor Matthew R. Buckley puts forth a truly wild hypothesis: It might be possible to build worlds out of dark matter.
Monday, July 17, 2017
A University of Washington-led international team of astronomers has used data gathered by the Kepler Space Telescope to observe and confirm details of the outermost of seven exoplanets or-biting the star TRAPPIST-1.They confirmed that the planet, TRAPPIST-1h, orbits its star every 18.77 days, is linked in its orbital path to its siblings and is frigidly cold. Far from its host star, the planet is likely uninhabit-able -- but it may not always have been so.
Monday, July 10, 2017
Relativistic Generalization of the Incentive Trap of Interstellar Travel with Application to Breakthrough Starshot
As new concepts of sending interstellar spacecraft to the nearest stars are now being investigated by various research teams, crucial questions about the timing of such a vast financial and labor investment arise. If humanity could build high-speed interstellar lightsails and reach α Centauri 20 yr after launch, would it be better to wait a few years, then take advantage of further technology improvements and arrive earlier despite waiting? The risk of being overtaken by a future, faster probe has been described earlier as the incentive trap. Based on 211 yr of historical data, we find that the speed growth of artificial vehicles, from steam-driven locomotives to Voyager 1, is much faster than previously believed, about 4.72 % annually or a doubling every 15 yr. We derive the mathematical framework to calculate the minimum of the wait time to launch t plus travel time τ(t) and extend it into the relativistic regime. We show that the t + τ(t) minimum disappears for nearby targets. There is no use of waiting once we can reach an object within about 20 yr of travel, irrespective of the actual speed. In terms of speed, the t + τ(t) minimum for a travel to α Centauri occurs at 19.6 % the speed of light (c), in agreement with the 20 % c proposed by the Breakthrough Starshot Initiative. If interstellar travel at 20 % c could be achieved within 45 yr from today and the kinetic energy be increased at a rate consistent with the historical record, then humans can reach the ten most nearby stars within 100 yr from today.
Friday, July 7, 2017
Proxima Centauri b may not be alone out there.The 2016 announcement of Proxima Centauri b was a watershed moment in exoplanet research. Not only had researchers found a potentially habitable Earth-mass planet, but it was at the nearest star to Earth. This means it could be one of the easiest systems to study using future telescopes.But researchers are now looking into some promising signals suggesting there are more planets lurking in the system.
Monday, July 3, 2017
Neutron Star Planets: Atmospheric processes and habitability
Patruno et al
Of the roughly 3000 neutron stars known, only a handful have sub-stellar companions. The most famous of these are the low-mass planets around the millisecond pulsar B1257+12. New evidence indicates that observational biases could still hide a wide variety of planetary systems around most neutron stars. We consider the environment and physical processes relevant to neutron star planets, in particular the effect of X-ray irradiation and the relativistic pulsar wind on the planetary atmosphere. We discuss the survival time of planet atmospheres and the planetary surface conditions around different classes of neutron stars, and define a neutron star habitable zone. Depending on as-yet poorly constrained aspects of the pulsar wind, both Super-Earths around B1257+12 could lie within its habitable zone.