105 research outputs found
Beyond Kepler: Direct Imaging of Exoplanets
The exoplanets field has been revolutionizing astronomy over the past 20+ years and shows no signs of stopping. The next big wave of exoplanet science may come from direct imaging of exoplanets. Several (non-habitable) exoplanets have already been imaged from the ground and NASA is planning an instrument for its 2020s flagship mission (WFIRST) to directly image large exoplanets. One of the key goals of the field is the detection and characterization of "Earth 2.0", i.e. a rocky planet with an atmosphere capable of supporting life. This appears possible with several potential instruments in the late 2020s such as WFIRST with a starshade, Extremely Large Telescopes (ELTs) from the ground, or one of NASA possible flagship missions in the 2030s (HabEx or LUVOIR). Also, if an Earth-like planet exists around Alpha Centauri (A or B), it may be possible to directly image it in the next approx. 5 years with a small space mission such as the Alpha Centauri Exoplanet Satellite (ACESat). I will describe the current challenges and opportunities in this exciting field, as well as the work we are doing at the Exoplanet Technologies group to enable this exciting science
Simulation of a method to directly image exoplanets around multiple stars systems
Direct imaging of extra-solar planets has now become a reality, especially
with the deployment and commissioning of the first generation of specialized
ground-based instruments such as the GPI, SPHERE, P1640 and SCExAO. These
systems will allow detection of planets 1e7 times fainter than their host star.
For space-based missions, such as EXCEDE, EXO-C, EXO-S, WFIRST-AFTA,
different teams have shown in laboratories contrasts reaching 1e-10 within a
few diffraction limits from the star using a combination of a coronagraph to
suppress light coming from the host star and a wavefront control system. These
demonstrations use a deformable mirror (DM) to remove residual starlight
(speckles) created by the imperfections of telescope. However, all these
current and future systems focus on detecting faint planets around a single
host star or unresolved binaries/multiples, while several targets or planet
candidates are located around nearby binary stars such as our neighbor star
Alpha Centauri.
Until now, it has been thought that removing the light of a companion star is
impossible with the current technology, excluding binary star systems from
target lists of direct imaging missions. Direct imaging around binaries or
multiples systems at a level of contrast allowing Earth-like planets detection
is challenging because the region of interest, where a dark zone is essential,
is contaminated by the light coming from the host star's companion. We propose
a method to simultaneously correct aberration sand diffraction of light coming
from the target star. This method works even if the companion star is outside
the control region of the DM (beyond its half-Nyquist frequency), by taking
advantage of aliasing effects.Comment: 8 pages, 13 figures, SPIE Astronomical Telescope and Instrumentation
conferenc
The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)
We present an overview of the EXoplanetary Circumstellar Environments and
Disk Explorer (EXCEDE), selected by NASA for technology development and
maturation. EXCEDE will study the formation, evolution and architectures of
exoplanetary systems, and characterize circumstellar environments into stellar
habitable zones. EXCEDE provides contrast-limited scattered-light detection
sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much smaller
effective inner working angle (IWA), thus enabling the exploration and
characterization of exoplanetary circumstellar disks in currently inaccessible
domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase
Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm
diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will
deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 L/D IWA or
140 mas with a wavefront control system utilizing a 2000-element MEMS DM and
fast steering mirror. EXCEDE will provide 120 mas spatial resolution at 0.4
microns with dust detection sensitivity to levels of a few tens of zodis with
two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder
that will advance our understanding of the formation and evolution of
exoplanetary systems, placing our solar system in broader astrophysical
context, and will demonstrate the high contrast technologies required for
larger-scale follow-on and multi-wavelength investigations on the road to
finding and characterizing exo-Earths in the years ahead
High Performance Lyot and PIAA Coronagraphy for Arbitrarily shaped Telescope Apertures
Two high performance coronagraphic approaches compatible with segmented and
obstructed telescope pupils are described. Both concepts use entrance pupil
amplitude apodization and a combined phase and amplitude focal plane mask to
achieve full coronagraphic extinction of an on-axis point source. While the
first concept, named Apodized Pupil Complex Mask Lyot Coronagraph (APCMLC),
relies on a transmission mask to perform the pupil apodization, the second
concept, named Phase-Induced Amplitude Apodization complex mask coronagraph
(PIAACMC), uses beam remapping for lossless apodization. Both concepts
theoretically offer complete coronagraphic extinction (infinite contrast) of a
point source in monochromatic light, with high throughput and sub-lambda/D
inner working angle, regardless of aperture shape. The PIAACMC offers nearly
100% throughput and approaches the fundamental coronagraph performance limit
imposed by first principles. The steps toward designing the coronagraphs for
arbitrary apertures are described for monochromatic light. Designs for the
APCMLC and the higher performance PIAACMC are shown for several monolith and
segmented apertures, such as the apertures of the Subaru Telescope, Giant
Magellan Telescope (GMT), Thirty Meter Telescope (TMT), the European Extremely
Large Telescope (E-ELT) and the Large Binocular Telescope (LBT). Performance in
broadband light is also quantified, suggesting that the monochromatic designs
are suitable for use in up to 20% wide spectral bands for ground-based
telescopes.Comment: 19 pages, 12 figures, accepted for publication in Ap
Beyond Kepler: Direct Imaging of Earth-like Planets
Is there another Earth out there? Is there life on it? People have been asking these questions for over two thousand years, and we finally stand on the verge of answering them. The Kepler space telescope is NASA's first mission designed to study Earthlike exoplanets (exo-Earths), and it will soon tell us how often exo-Earths occur in the habitable zones of their stars. The next natural step after Kepler is spectroscopic characterization of exo-Earths, which would tell us whether they possess an atmosphere, oxygen, liquid water, as well as other biomarkers. In order to do this, directly imaging an exo-Earth may be necessary (at least for Sun-like stars). Directly imaging an exo-Earth is challenging and likely requires a flagship-size optical space telescope with an unprecedented imaging system capable of achieving contrasts of 1(exp 10) very close to the diffraction limit. Several coronagraphs and external occulters have been proposed to meet this challenge and are in development. After first overviewing the history and current state of the field, my talk will focus on the work proceeding at the Ames Coronagraph Experiment (ACE) at the NASA Ames Research Center, where we are developing the Phase Induced Amplitude Apodization (PIAA) coronagraph in a collaboration with JPL. PIAA is a powerful technique with demonstrated aggressive performance that defines the state of the art at small inner working angles. At ACE, we have achieved contrasts of 2(exp -8) with an inner working angle of 2 lambda/D and 1(exp -6) at 1.4 lambda/D. On the path to exo-Earth imaging, we are also pursuing a smaller telescope concept called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which was recently selected for technology development (Category III) by NASA's Explorer program. EXCEDE will do fundamental science on debris disks as well as serve as a technological and scientific pathfinder for an exo-Earth imaging mission
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