10. July 2015

'Close up' with Plu­to – NASA New Hori­zons ar­rival im­mi­nent

New Hori­zons reach­es Plu­to and Charon
Image 1/4, Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).

New Horizons reaches Pluto and Charon

On 14 Ju­ly 2015, the NASA space­craft New Hori­zons will fly past the dwarf plan­et Plu­to and its com­pan­ion, Charon. For the first time, an ob­ject in the Kuiper-Edge­worth belt of the So­lar Sys­tem will be ex­plored up close. New Hori­zons will pass Plu­to at a dis­tance of 12,500 kilo­me­tres, as shown in this artist’s im­pres­sion.
New Hori­zons has ac­quired colour im­ages of Plu­to
Image 2/4, Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).

New Horizons has acquired colour images of Pluto

On 14 Ju­ly 2015, the NASA New Hori­zons space­craft will fly past the dwarf plan­et Plu­to. Al­ready from 15 mil­lion kilo­me­tres away, im­ages ac­quired by the LOR­RI in­stru­ment on board New Hori­zons, which were com­bined with colour in­for­ma­tion from the Ralph cam­era sys­tem, show a sur­pris­ing num­ber of de­tails on the sur­face of Plu­to and its com­pan­ion, the moon Charon. Plu­to has a di­am­e­ter of ap­prox­i­mate­ly 2380 kilo­me­tres; Charon is about 1200 kilo­me­tres across. The im­ages were ac­quired be­tween 23 and 29 June 2015.
Plu­to’s north­ern hemi­sphere in colour – ‘red­dish brown’ dwarf plan­et
Image 3/4, Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).

Pluto’s northern hemisphere in colour – ‘reddish brown’ dwarf planet

As­tronomers have on­ly been able to get a very vague idea of the sur­face of Plu­to us­ing ground-based ob­ser­va­to­ries and im­ages ac­quired by the Hub­ble Space Tele­scope. This first map of the north­ern hemi­sphere of Plu­to is de­rived from da­ta ac­quired by New Hori­zons dur­ing the ap­proach phase, from a dis­tance of more than 10 mil­lion kilo­me­tres; they show the dwarf plan­et in near true colour. High-res­o­lu­tion monochrome im­ages from the LOR­RI in­stru­ment were used to pro­duce the an­i­ma­tion on the left. The map pro­jec­tion on the right in­cludes colour in­for­ma­tion from the cam­era sys­tem Ralph. For the cen­tre an­i­ma­tion, both da­ta sets were com­bined.
A tiny, mov­ing point of light – the dis­cov­ery of Plu­to
Image 4/4, Credit: Lowell Observatory.

A tiny, moving point of light – the discovery of Pluto

Ev­ery pupil in the US is taught the sto­ry of the dis­cov­ery of Plu­to. In 1905, the US as­tronomer Per­ci­val Low­ell (1855–1916) sug­gest­ed that the per­tur­ba­tions of Nep­tune’s or­bit re­quired the ex­is­tence of a ninth plan­et. For 11 years, Low­ell tried to find this ce­les­tial body, but was un­able to do so. The ob­ser­va­tion did not come un­til 14 years af­ter Low­ell’s death, through a young re­search as­sis­tant named Clyde Tombaugh. For many weeks dur­ing the win­ter of 1929/1930, Tombaugh con­duct­ed ob­ser­va­tions at the Low­ell Ob­ser­va­to­ry in Flagstaff (Ari­zona) – named af­ter the fa­mous as­tronomer – of the ar­eas of the sky where it had been sug­gest­ed that the plan­et would be lo­cat­ed. On 18 Febru­ary 1930, us­ing a blink com­para­tor pro­duced by Carl Zeiss in Je­na, Ger­many, Tombaugh dis­cov­ered a mov­ing spot on two pho­to­graph­ic plates. The dis­cov­ery was an­nounced on 13 March – Low­ell’s birth­day.

DLR supports German scientists in the REX radio experiment

After a nine-and-a half year journey, the NASA New Horizons spacecraft will fly past the dwarf planet Pluto – approximately 4.8 billion kilometres from Earth – at 13:50 CEST on 14 July 2015. This is the first time that the former 'ninth planet' in the Solar System will receive a visitor. It is also the first time that this celestial body will be examined 'up close', at a distance of roughly 12,500 kilometres, and less than Earth’s diameter.

Seven scientific experiments will record images, spectra and physical measurement values during the flyby phase. On board the spacecraft are two plasma instruments (PEPSSI and SWAP), one dust detector (Venetia), a radio experiment (REX) and three optical devices: the UV spectrometer Alice and the LORRI and Ralph high-resolution camera systems. REX will use radio waves to examine the atmospheres and determine the surface temperatures and masses of Pluto and its largest moon, Charon. It is the only instrument on New Horizons that involves a contribution by German scientists, namely the planetary researchers at the Rhenish Institute for Environmental Research at the University of Cologne (EURAD).

The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration has supported Martin Pätzold’s participation in the REX experiment with funds provided by the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi). "Our role here is to act as co-investigators, which means we will conduct two experiments while New Horizons flies past Pluto," reports Pätzold, who is experiencing the 'hot phase' of the mission in the Applied Physics Laboratory (APL) at Johns Hopkins University in Laurel (Maryland), USA, the institute responsible for implementing and controlling the mission on behalf of NASA. "We will measure the surface temperatures on Pluto and its moon Charon in the microwave range. We also want to directly determine the masses and densities of Pluto and Charon. Mass and density provide important insights into the inner structure of planetary bodies and their origin," Pätzold continues.

REX is the first experiment in which radio signals are sent to a spacecraft from Earth; standard practice is for a spacecraft to send radio signals to Earth for analysis. In this case, however, the intention is for REX to measure a deflection and weakening of the signals sent from Earth caused by the possible thin atmospheres surrounding Pluto and Charon. This could permit conclusions to be drawn about the temperatures and pressures prevailing close to the surfaces.

An icy body, one billion kilometres from the Sun

"Pluto, which has a diameter of approximately 2310 kilometres, and its slightly smaller companion, Charon, are almost entirely uncharted terrain for planetary researchers; this is why scientists around the world are waiting excitedly to receive the images and measurements of New Horizons," says Tilman Spohn, Director of the DLR Institute of Planetary Research in Berlin.

The scientists hope that the images will help them understand the geology and the underlying processes of Pluto and Charon. In addition, the surface constituents will be subjected to geochemical and mineralogical analysis. The thin atmosphere, consisting of vaporised ice compounds, will also be examined. Furthermore, there are hopes that the geophysical measurements will help decode the inner structure of Pluto and Charon's dual-body system.

"Pluto may even be a suitable object to search for ecological niches in which the development of simple life forms would be conceivable," says Spohn, adding: "Pluto is the largest known object in the Edgeworth-Kuiper belt, a zone five to 10 billion kilometres from the Sun, beyond Neptune's orbit, inhabited by icy bodies, approximately. As is the case with asteroids and comets, the absence of geological processes has left these 'ice dwarfs' practically unaltered since the first days of their emergence. This means that Pluto could have a lot to teach us about the earliest era of the Solar System, just like Comet 67P, which we are currently investigating using the Rosetta orbiter."

However, the extremely high speed – roughly 50,000 kilometres per hour – at which New Horizons is approaching Pluto makes it technically impossible to enter orbit.

APL expects the first close-up images of Pluto and Charon to be available on 15 July 2015. However, the long signal propagation delay in radio communication with the spacecraft, which is almost four-and-a-half hours one-way, means it will take over a year before the onboard computer has transmitted all the scientific data to Earth.

  • The fastest spacecraft of all time

    New Horizons was launched from Cape Canaveral (Florida) on 19 January 2006. The approximately 500-kilogram orbiter flew past Jupiter on 28 February 2007; the flyby accelerated the spacecraft to its final speed; the flyby of Pluto and Charon will take place at 50,400 kilometres per hour, making New Horizons the fastest spacecraft ever to travel across the Solar System. Like the far away planets Uranus and Neptune, Pluto is not visible with the naked eye from Earth. In 2006, the International Astronomical Union reclassified Pluto as a dwarf planet. The main argument was that Pluto has not yet removed from its orbit other, smaller bodies, which is what the eight other 'classic' planets have achieved. New Horizons started its observations of Pluto and Charon in January 2015. The dwarf planet has five moons in total, but so far there have been few meaningful telescope observations of the entire Pluto system, and only a small number of images acquired using the Hubble Space Telescope.

  • Elisabeth Mittelbach
    Ger­man Aerospace Cen­ter (DLR)
    Com­mu­ni­ca­tions, Space Ad­min­is­tra­tion
    Telephone: +49 228 447-385
    Fax: +49 228 447-386
    Königswinterer Str. 522-524
    53227 Bonn
  • Ulrich Köhler
    Pub­lic re­la­tions co­or­di­na­tor
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-215
    Fax: +49 30 67055-402
    Rutherfordstraße 2
    12489 Berlin
  • Prof.Dr. Tilman Spohn
    HP³ Prin­ci­pal In­ves­ti­ga­tor
    Ger­man Aerospace Cen­ter (DLR)

    DLR In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-300
    Fax: +49 30 67055-303
    Linder Höhe
    51147 Köln
  • Martin Pätzold
    Rhen­ish In­sti­tute for En­vi­ron­men­tal Re­search at the Uni­ver­si­ty of Cologne (EU­RAD)
    Plan­e­tary Sci­ence
    Telephone: +49 170 2947-318

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