Starshade Deployed At JPL 2014 PIA20909
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The New Worlds Mission is a proposed project comprising a large
occulter An occulting disk is a small disk used in a telescope to block the view of a bright object in order to allow observation of a fainter one. The coronagraph, at its simplest, is an occulting disk in the focal plane of a telescope, or in front of th ...
flying in formation with a space telescope designed to block the light of nearby
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s in order to observe their orbiting exoplanets. The observations could be taken with an existing space telescope or a dedicated visible light
optical telescope An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electro ...
optimally designed for the task of finding exoplanets. A preliminary research project was funded from 2005 through 2008 by NASA Institute for Advanced Concepts (NIAC) and headed by Webster Cash of the
University of Colorado at Boulder The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a public research university in Boulder, Colorado. Founded in 1876, five months before Colorado became a state, it is the flagship university of the University of Colorado sys ...
in conjunction with Ball Aerospace & Technologies Corp.,
Northrop Grumman Northrop Grumman Corporation is an American multinational aerospace and defense technology company. With 90,000 employees and an annual revenue in excess of $30 billion, it is one of the world's largest weapons manufacturers and military techn ...
,
Southwest Research Institute Southwest Research Institute (SwRI), headquartered in San Antonio, Texas, is an independent and nonprofit applied research and development (R&D) organization. Founded in 1947 by oil businessman Tom Slick, it provides contract research and develop ...
and others. Since 2010 the project has been looking for additional financing from NASA and other sources in the amount of roughly US$3 billion including its own four-meter telescope.
-
arcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
. Angles this small are impossible to resolve from the ground due to astronomical seeing. *Exoplanets being extremely dim compared to their host stars. Typically, the star will be approximately a billion times brighter than the orbiting planet. This makes it nearly impossible to see planets against the star's glare. The difficulty of observing such a dim planet so close to a bright star is the obstacle that has prevented astronomers from directly photographing exoplanets. To date, only a handful of exoplanets have been photographed. The first exoplanet to be photographed,
2M1207b 2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.
, is in orbit around a star called
2M1207 2M1207, 2M1207A or 2MASSW J12073346–3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered ...
. Astronomers were only able to photograph this planet because it is a very unusual planet that is very far from its host star, approximately 55 astronomical units (about twice the distance of
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
). Furthermore, the planet is orbiting a very dim star, known as a
brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
. To overcome the difficulty of distinguishing more Earth-like planets in the vicinity of a bright star, the New Worlds Mission would block the star's light with an
occulter An occulting disk is a small disk used in a telescope to block the view of a bright object in order to allow observation of a fainter one. The coronagraph, at its simplest, is an occulting disk in the focal plane of a telescope, or in front of th ...
. The occulter would block all of the starlight from reaching the observer, while allowing the planet's light to pass undisturbed. The starshade would be tens of meters across and probably made out of
Kapton Structure of poly-oxydiphenylene-pyromellitimide Kapton insulating pads for mounting electronic parts on a heat sink Kapton is a polyimide film used in flexible printed circuits (flexible electronics) and space blankets, which are used on spac ...
, a lightweight material similar to Mylar.


Methods

Traditional methods of exoplanet detection rely on indirect means of inferring the existence of orbiting bodies. These methods include: *
Astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...
– watching a star move slightly due to the gravitational influence of a nearby planet *Observing Doppler shifts of the star's spectrum due to the star's movement *Observing the amount of light from a star change as an extrasolar planet transits the star, preventing a portion of the light from reaching the observer *
Pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...
timing * Gravitational microlensing *Observing radiation from circumstellar disks in the
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
All of these methods provide convincing evidence for the existence of extrasolar planets, but none of them provide actual images of the planets. The goal of the New Worlds Mission is to block the light coming from nearby stars with an occulter. This would allow the direct observation of orbiting planets. The occulter would be a large sheet disc flown thousands of kilometers along the line of sight. The disc would likely be several tens of meters in diameter and would fit inside existing
expendable launch vehicles An expendable launch system (or expendable launch vehicle/ELV) is a launch vehicle that can be launched only once, after which its components are either destroyed during reentry or discarded in space. ELVs typically consist of several rocket sta ...
and be deployed after launch. One difficulty with this concept is that light incoming from the target star would diffract around the disc and constructively interfere along the central axis. Thus the starlight would still be easily visible, making planet detection impossible. This concept was first famously theorized by Siméon Poisson in order to disprove the wave theory of light, as he thought the existence of a bright spot at the center of the shadow to be nonsensical. However
Dominique Arago "Dominique" is a 1963 French language popular song, written and performed by the Belgian female singer Jeannine Deckers, better known as Sœur Sourire ("Sister Smile" in French) or The Singing Nun. The song is about Saint Dominic, a Spanish-bo ...
experimentally verified the existence of the spot of Arago. This effect can be negated by specifically shaping the occulter. By adding specially shaped petals to the outer edge of the disc, the spot of Arago will disappear, allowing the suppression of the star's light. This technique would make planetary detection possible for stars within approximately 10
parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...
(about 32 light years) of Earth. It is estimated that there could be several thousand exoplanets within that distance. The starshade is similar to but should not be confused with the
Aragoscope An Aragoscope is a telescope design based on diffraction around the edge of an occluding disc, named after French scientist François Arago. Concept The light diffracted around the edge of a perfectly circular occluder interferes constructively at ...
, which is a proposed imaging device designed to use the diffraction of light around a perfectly-circular light-shield to produce an image. The starshade is a proposed
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
-shaped coronagraph disc that was designed to block starlight that interferes with
telescopic A telescope is an instrument designed for the observation of remote objects. Telescope(s) also may refer to: Music * The Telescopes, a British psychedelic band * ''Telescope'' (album), by Circle, 2007 * ''The Telescope'' (album), by Her Space H ...
observations of other worlds. The "petals" of the "sunflower" shape of the starshade are designed to eliminate the diffraction that is the central feature of an
Aragoscope An Aragoscope is a telescope design based on diffraction around the edge of an occluding disc, named after French scientist François Arago. Concept The light diffracted around the edge of a perfectly circular occluder interferes constructively at ...
. The starshade is a
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
designed by Webster Cash, an astrophysicist at the
University of Colorado at Boulder The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a public research university in Boulder, Colorado. Founded in 1876, five months before Colorado became a state, it is the flagship university of the University of Colorado sys ...
's Center for Astrophysics and Space Astronomy. The proposed spacecraft was designed to work in tandem with space telescopes like the
James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Spa ...
, which did not use it, or a new 4-meter telescope. It would fly in front of a space telescope (between the telescope and a target
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
) and approximately away from Earth, outside of Earth's
heliocentric Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth at ...
orbit. When unfurled, the starshade resembles a
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
, with pointed protrusions around its circumference. The starshade acts as a very large coronagraph: it blocks light of a distant star, making it easier to observe associated planets. The unfurled starshade could reduce collected light from bright stars by as much as 10 billion-fold. Light that "leaks" around the edges would be used by the telescope as it scans the target system for
planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...
. With the reduction of the harsh light, astronomers will be able to check exoplanet atmospheres tens of trillions of miles away for the potential chemical signatures of
life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
.CU Proposal To Image Distant Planets Is Funded For Second Round Of Study


Objectives

The New Worlds Mission aims to discover and analyze terrestrial extrasolar planets: #Detection: First, using the space telescope and 'starshade', or occulter, exoplanetary systems will be directly detected. #System mapping: Following detection, system mapping would involve the direct mapping of planetary systems through the detection of the planetary light separate from the parent star. In a sufficiently high-quality image, planets would appear as individual star-like objects. A series of images of the planetary system would allow measurements of planetary orbits, and the brightness and broadband colors of the planets would provide information about their basic nature. #Planet studies: At this stage, detailed study of individual planets would take place. With a low noise level and a modest signal,
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
and
photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electrom ...
can be performed. Spectroscopy allows scientists to perform chemical analysis of
atmospheres The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level. History The s ...
and surfaces, which might hold clues to the existence of
life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
elsewhere in the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
. Photometry will show variation in color and intensity as surface features rotate in and out of the field of view, allowing for the detection of oceans, continents, polar caps and clouds. #Planet imaging: A large increase in capability is needed to achieve true planet imaging. However, techniques of
interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
show that, in principle, this is possible to achieve. Fifty to one hundred percent of a planet's surface could theoretically be mapped, depending on the planet's
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
. #Planetary assessment: The final step in extrasolar planet studies would be the ability to study these distant worlds in the same way that Earth-observing systems study the Earth's surface. Such a telescope would need to be extremely large, to collect enough light to resolve and analyze small details on the planet's surface. However, these kinds of studies do not lie in the foreseeable future, for it takes square kilometers of collecting area to capture the needed signal. In addition to finding and analyzing terrestrial planets, it can also discover and analyze gas giants. The New Worlds Mission will also find moons and rings orbiting extrasolar planets. This technique will involve direct imaging of planets by blocking the starlight with a starshade. It will study the moons and rings in detail and find whether moons can also support life if gas giant planets orbit in the habitable zones of parent stars.


Architecture

There are many possibilities for various New Worlds Missions, three of which are: #New Worlds Discoverer proposed to use an existing space telescope (like the James Webb telescope), to find exoplanets. The size of the starshade could be optimized for the observing telescope. #New Worlds Observer would use two spacecraft, one that has a dedicated telescope and one with a starshade to find exoplanets. The possibility of two starshades is also a consideration. One starshade to point towards the desired target while the other moves into position for the next target. This would eliminate some of the time delay in observing different systems and allow for many more targets to be observed in the same timespan. #New Worlds Imager would use many spacecraft/starshades. This would allow observers to resolve the planet and obtain true planetary imaging.


See also

* Coronagraph, a telescopic attachment to block out the light from a star so that nearby objects can be resolved *
Space sunshade A space sunshade or sunshield is a parasol that diverts or otherwise reduces some of the Sun's radiation, preventing it from hitting a spacecraft or planet and thereby reducing its insolation, which results in reduced heating. Light can be div ...
*
Aragoscope An Aragoscope is a telescope design based on diffraction around the edge of an occluding disc, named after French scientist François Arago. Concept The light diffracted around the edge of a perfectly circular occluder interferes constructively at ...


References


External links


New World's official website at University of Colorado, BoulderFinding planets through a pinhole
{{Exoplanet search projects Diffraction Exoplanet search projects Proposed spacecraft Space telescopes Articles containing video clips NASA programs