New Horizons Halfway to Pluto

In 2006, NASA dispatched an ambassador to the planetary frontier. The New Horizons spacecraft is now halfway between Earth and Pluto, on approach for a dramatic flight past the icy planet and its moons in July 2015.

After 10 years and more than 3 billion miles, on a historic voyage that has already taken it over the storms and around the moons of Jupiter, New Horizons will shed light on new kinds of worlds we’ve only just discovered on the outskirts of the solar system.

Pluto gets closer by the day, and New Horizons continues into rare territory, as just the fifth probe to traverse interplanetary space so far from the Sun. And the first to travel so far, to reach a new planet for exploration. nasa.gov


http://youtu.be/B1585CMqdVw

New evidence for complex molecules on Pluto’s surface

Southwest Research Institute (SwRI)

The Cosmic Origins Spectrograph aboard NASA's Hubble Space Telescope recently discovered a strong ultraviolet-wavelength absorber on Pluto's surface.

The new and highly sensitive Cosmic Origins Spectrograph aboard the Hubble Space Telescope has discovered a strong ultraviolet-wavelength absorber on Pluto’s surface, providing new evidence that points to the possibility of complex hydrocarbon and/or nitrile molecules lying on the surface, according to a paper recently published in the Astronomical Journal by researchers from Southwest Research Institute and Nebraska Wesleyan University.

Such chemical species can be produced by the interaction of sunlight or cosmic rays with Pluto’s known surface ices, including methane, carbon monoxide and nitrogen.

The project, led by SwRI’s Dr. Alan Stern, also included SwRI researchers Dr. John Spencer and Adam Shinn, and Nebraska Wesleyan University researchers Dr. Nathaniel Cunningham and student Mitch Hain.

“This is an exciting finding because complex Plutonian hydrocarbons and other molecules that could be responsible for the ultraviolet spectral features we found with Hubble may, among other things, be responsible for giving Pluto its ruddy color,” said Stern.

The team also discovered evidence of changes in Pluto’s ultraviolet spectrum compared to Hubble measurements from the 1990s. The changes may be related to differing terrains seen now versus in the 1990s, or to other effects, such as changes in the surface related to a steep increase in the pressure of Pluto’s atmosphere during that same time span.

“The discovery we made with Hubble reminds us that even more exciting discoveries about Pluto’s composition and surface evolution are likely to be in store when NASA’s New Horizons spacecraft arrives at Pluto in 2015,” Stern added.
www.swri.org

Faraway Eris is Pluto’s Twin

Dwarf planet sized up accurately as it blocks light of faint star

Artist’s impression of the dwarf planet Eris

Astronomers have accurately measured the diameter of the faraway dwarf planet Eris for the first time by catching it as it passed in front of a faint star. This event was seen at the end of 2010 by telescopes in Chile, including the Belgian TRAPPIST telescope at ESO’s La Silla Observatory. The observations show that Eris is an almost perfect twin of Pluto in size. Eris appears to have a very reflective surface, suggesting that it is uniformly covered in a thin layer of ice, probably a frozen atmosphere. The results will be published in the 27 October 2011 issue of the journal Nature.

In November 2010, the distant dwarf planet Eris passed in front of a faint background star, an event called an occultation. These occurrences are very rare and difficult to observe as the dwarf planet is very distant and small. The next such event involving Eris will not happen until 2013. Occultations provide the most accurate, and often the only, way to measure the shape and size of a distant Solar System body.

The candidate star for the occultation was identified by studying pictures from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory. The observations were carefully planned and carried out by a team of astronomers from a number of (mainly French, Belgian, Spanish and Brazilian) universities using — among others — the TRAPPIST [1] (TRAnsiting Planets and PlanetesImals Small Telescope, eso1023) telescope, also at La Silla.

“Observing occultations by the tiny bodies beyond Neptune in the Solar System requires great precision and very careful planning. This is the best way to measure Eris’s size, short of actually going there,” explains Bruno Sicardy, the lead author.

Observations of the occultation were attempted from 26 locations around the globe on the predicted path of the dwarf planet’s shadow — including several telescopes at amateur observatories, but only two sites were able to observe the event directly, both of them located in Chile. One was at ESO’s La Silla Observatory using the TRAPPIST telescope, and the other was located in San Pedro de Atacama and used two telescopes [2]. All three telescopes recorded a sudden drop in brightness as Eris blocked the light of the distant star.

The combined observations from the two Chilean sites indicate that Eris is close to spherical. These measurements should accurately measure its shape and size as long as they are not distorted by the presence of large mountains. Such features are, however, unlikely on such a large icy body.

Eris was identified as a large object in the outer Solar System in 2005. Its discovery was one of the factors that led to the creation of a new class of objects called dwarf planets and the reclassification of Pluto from planet to dwarf planet in 2006. Eris is currently three times further from the Sun than Pluto.

While earlier observations using other methods suggested that Eris was probably about 25% larger than Pluto with an estimated diameter of 3000 kilometres, the new study proves that the two objects are essentially the same size. Eris’s newly determined diameter stands at 2326 kilometres, with an accuracy of 12 kilometres. This makes its size better known than that of its closer counterpart Pluto, which has a diameter estimated to be between 2300 and 2400 kilometres. Pluto’s diameter is harder to measure because the presence of an atmosphere makes its edge impossible to detect directly by occultations. The motion of Eris’s satellite Dysnomia [3] was used to estimate the mass of Eris. It was found to be 27% heavier than Pluto [4]. Combined with its diameter, this provided Eris’s density, estimated at 2.52 grams per cm3 [5].

“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” comments Emmanuel Jehin, who contributed to the study [6].

The surface of Eris was found to be extremely reflective, reflecting 96% of the light that falls on it (a visible albedo of 0.96 [7]). This is even brighter than fresh snow on Earth, making Eris one of the most reflective objects in the Solar System, along with Saturn’s icy moon Enceladus. The bright surface of Eris is most likely composed of a nitrogen-rich ice mixed with frozen methane — as indicated by the object’s spectrum — coating the dwarf planet’s surface in a thin and very reflective icy layer less than one millimetre thick.

“This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the Sun in its elongated orbit and into an increasingly cold environment,” Jehin adds. The ice could then turn back to gas as Eris approaches its closest point to the Sun, at a distance of about 5.7 billion kilometres.

The new results also allow the team to make a new measurement for the surface temperature of the dwarf planet. The estimates suggest a temperature for the surface facing the Sun of -238 Celsius at most, and an even lower value for the night side of Eris.

“It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes. Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members,” concludes Bruno Sicardy.

Notes

[1] TRAPPIST is one of the latest robotic telescopes installed at the La Silla Observatory. With a main mirror just 0.6 metres across, it was inaugurated in June 2010 and is mainly dedicated to the study of exoplanets and comets. The telescope is a project funded by the Belgian Fund for Scientific Research (FRS-FNRS), with the participation of the Swiss National Science Foundation, and is controlled from Liège.

[2] The Caisey Harlingten and ASH2 telescopes.

[3] Eris is the Greek goddess of chaos and strife. Dysnomia is Eris’ daughter and the goddess of lawlessness.

[4] Eris’s mass is 1.66 x 1022 kg, corresponding to 22% of the mass of the Moon.

[5] For comparison, the Moon’s density is 3.3 grams per cm3, and water’s is 1.00 gram per cm3.

[6] The value of the density suggests that Eris is mainly composed of rock (85%), with a small ice content (15%). The latter is likely to be a layer, about 100 kilometre thick, that surrounds the large rocky core. This very thick layer of mostly water ice is not to be confused with the very thin layer of frozen atmosphere on Eris’s surface that makes it so reflective.

[7] The albedo of an object represents the fraction of the light that falls on it that is scattered back into space rather than absorbed. An albedo of 1 corresponds to perfect reflecting white, while 0 is totally absorbing black. For comparison, the Moon’s albedo is only 0.136, similar to that of coal.

More information

This research was presented in a paper to appear in the 27 October 2011 issue of the journal Nature.

www.eso.org

Pluto’s icy exterior may conceal an ocean

PLUTO could hide a liquid ocean beneath its icy shell. Indeed, other bodies on the solar system’s frigid fringe could also harbour subsurface oceans, and these could provide the conditions to sustain life.

Temperatures on Pluto’s surface hover around -230 °C, but researchers have long wondered whether the dwarf planet might boast enough internal heat to sustain a liquid ocean under its icy exterior.

Now Guillaume Robuchon and Francis Nimmo at the University of California, Santa Cruz, say there is a good chance it does. They calculate that an ocean depends on two things: the amount of radioactive potassium in Pluto’s rocky core, and the sloshiness of the ice that covers it.

Density measurements suggest a rocky core fills 40 per cent of the dwarf planet’s volume. If the core contains potassium at a concentration of 75 parts per billion, its decay could produce enough heat to melt some of the overlying ice, which is made of a mixture of nitrogen and water.

It should have at least that much potassium and probably more, says William McKinnon at Washington University in St Louis, Missouri. He points out that Earth, which probably formed with less of the volatile element due to its closer distance to the sun, has 10 times that concentration in its core.

But merely having a source of heat is not enough to maintain a long-lived ocean. Heat from the core will trigger convection in the surrounding ice, and if the ice churns too quickly, the heat will simply escape into space before it can do much melting. If it flows substantially more slowly than Antarctic glaciers on Earth, however, then the top 165 kilometres of ice could provide enough insulation for a liquid ocean of the same depth to exist below, the team calculates (Icarus, DOI: 10.1016/j.icarus.2011.08.015).

The viscosity of the ice depends on the size of individual ice particles, with smaller grains flowing more easily. There is no way to measure this from Earth, but Pluto’s shape could reveal evidence of an ocean, the team says. Pluto’s spin is slowing down due to tugs from its large moon Charon. Fast-spinning objects bulge out at their equator, but a soft interior would allow the world to relax into more of a sphere as its spin slows down. NASA’s New Horizons probe will image the dwarf planet’s shape when it flies past in 2015.

Other distant icy bodies might also have oceans, which could mean that the outer solar system is potentially ripe for life. “It’s very exciting to think that these dwarf planets could have astrobiological potential,” says New Horizons lead scientist Alan Stern.

http://www.newscientist.com/article/mg21128303.900-plutos-icy-exterior-may-conceal-an-ocean.html

Are there rings around Pluto?

Considering effects of tidal plus centrifugal stress acting on icy-rocks and the tensile strength thereof, icy-rocks being in the density range (1-2.4) g cm-3 which had come into existence as collisional ejecta (debris) in the vicinity of Pluto at the time when Pluto-Charon system came into being as a result of a giant impact of a Kuiper Belt Object on the primordial Pluto, it is shown, here, that these rocks going around Pluto in its vicinity are under slow disruption generating a stable ring structure consisting of icy-rocks of diameters in the range (20-90) km, together with fine dust and particles disrupted off the rocks, and spread all over the regions in their respective Roche Zones, various Roche radii being in ~1/2 three-body mean motion resonance. Calculations of gravitational spheres of influence of Pluto which turns out to be 4.2 x 106 km for prograde orbits and 8.5 x 106 km for retrograde orbits together with the existence of Kuiper Belt in the vicinity of Pluto assure that there may exist a few rocks (satellites)/dust rings/sheets so far undiscovered moving in prograde orbits around the planet and few others which are distant ones and move around Pluto in the region between 4.2×106 km and 8.5×106 km in retrograde orbits.

http://arxiv.org/abs/1109.1614

12 August 1930: Pluto: the new planet

Originally published in the Manchester Guardian on 12 August 1930

Computer-generated map of Pluto from Hubble images, synthesised true colour and among the highest resolutions possible with current technology

It would seem all doubts as to the existence of the new planet announced from the Lowell Observatory in March last have been set at rest. Fifteen years ago the late Dr. Percival Lowell published his “Memoir on a Trans Neptunian Planet,” in which he not only demonstrated that such a planet must exist but that certain small “residual perturbations” of the planet Uranus were satisfactorily explained by its existence. He also computed for the new planet a period of about 282 years, a distance of over 3,720,000,000 miles from the sun, a mass seven or eight times that of the earth, and an apparent brightness of the twelfth or thirteenth stellar magnitude. He further showed that the new planet was likely to be located in one or other of two regions of the sky – Gemini or Sagittarius.

For years the planet has been searched for at the Lowell Observatory. Not till early this year did the Lowell astronomers succeed in detecting in the constellation Gemini a faint moving star-like point, which seemed to answer the description of the long-looked-for planet, and on March 13, Dr. V. M. Slipher, Dr. Lowell’s successor as director of the observatory, felt sufficiently confident to announce the discovery of Lowell’s trans-Neptunian planet. However, doubts began to accumulate as to whether the newly discovered body was really Lowell’s planet. That it was a moving body belonging to the solar system no one could deny, but it might be in reality a very distant comet. A planet as massive as that postulated by Dr. Lowell – a body with a diameter of about 16,000 miles – ought to be considerably brighter than the fifteenth magnitude, unless its albedo, or reflective capacity, were very low, which is highly improbable.

Meanwhile astronomers began to examine photographs of the Gemini region of the sky taken over a period of years, with a view to finding the image of the planet. On a plate taken at the Uccle Observatory in Belgium on 27 January 1927, an image was detected which bore a striking resemblance to the new planet, and which has been, with great probability, presumed to be actually the planet. Making use of the Uccle observation, Dr. Crommelin was able to compute an orbit for the planet which turned out to be surprisingly similar to the orbit calculated by Lowell. Images of the new planet have since been found on plates taken at Mount Wilson in December, 1919.

Dr. Crommelin at the June meeting of the Royal Astronomical Society said: “At the April meeting we thought Lowell’s prediction was a fluke, but I do not think so now.” The one error made by Lowell was to overestimate the mass. Dr. Slipher has given the new body the name Pluto
http://www.guardian.co.uk