ESA’s DARWIN Proposal Online

by Paul Gilster on July 26, 2007

The European Space Agency’s DARWIN mission proposal is now available online, well worth a look if you’re hoping to keep up with planet-hunter spacecraft technologies. With a launch date dependent upon the evolution of its technology, DARWIN probably won’t get off for another decade, but with a primary goal of detecting and studying terrestrial planets around other stars, it is sure to be a high-visibility mission as it continues development.

DARWIN proposal cover

According to the proposal, the baseline DARWIN mission is to last five years and will target approximately 200 individual stars at mid-infrared wavelengths. The focus is on stellar types F, G, K and some M stars (about ten percent of the total). Of these, between twenty-five and fifty planets will be studied spectroscopically for evidence of gases such as CO2, O3 and H20. The mission planners are currently assuming the number of terrestrial planets in the habitable zone is one per system, adding that data from NASA’s Kepler mission will be useful in evaluating this conclusion.

And note this from the report:

…nearby K and M dwarfs are the easiest targets in terms of Earth-like planet detection for a given integration time. This is because the thermal infrared luminosity of a planet in the Habitable Zone depends only on its size. On the other hand, the stellar luminosity is a strong function of its spectral type. This means that the star/planet contrast varies with spectral type. Compared to the case of the Sun and Earth, this contrast is two times higher for F stars, a factor of three lower for K stars, and more than an order of magnitude lower for M dwarfs. Nevertheless, Darwin will focus on solar-type G type stars (50% of the observing time), and a significant number of them can be screened and any discovered terrestrial planets studied.

To retrieve the faint emission of a terrestrial planet from the nearby starshine, ESA estimates a 100-meter telescope would be required, a vast undertaking not currently within our technological limits. So DARWIN turns to four collector spacecraft feeding light to a ‘beam combiner’ craft. The chosen interferometer array is called Emma, and it allows the formation-flying telescopes to perform like a single, larger instrument.

M dwarf DARWIN studies

The diameter of the collector telescopes is a key issue: With 1-meter telescopes, the number of targets screened is reduced to about 75; with 3-meter mirrors, 2/3 of the catalog of stars compiled as possible targets can be examined. The report notes the potential for spurious signals from residual starlight (stellar leakage), the local zodiacal background produced by dust particles around our own Sun, the exo-zodiacal light from the target star’s dust disk, and the instrumental background produced by thermal emissions within the instruments. Details are in the report, but this is enough to suggest the magnitude of the detection task.

Image: Mass ejections and winds from low mass M and K-type stars can erode the atmosphere of planets in the habitable zone. Darwin will study how such activity influences the magnetic dynamo, atmosphere, and biology of these planets. Credit: DARWIN Mission Proposal.

Keep your eye on missions that have a direct impact on DARWIN:

  • COROT, already operational, should be able to detect planets down to about two Earth radii that orbit close to their stars (orbital period in the range of fifty days). COROT data should help firm up our ideas about the abundance of hot, rocky worlds around the stellar types under study.
  • NASA’s Kepler mission, scheduled for launch within the next two years, is designed to detect terrestrial planets near the habitable zones of the stars it studies. 100,000 main sequence stars will ultimately be monitored, with the spacecraft continually pointing its telescope at a single field looking for Earth-sized planetary transits. As Kepler proceeds, the statistical data on terrestrial worlds should become more and more reliable, allowing more fine-tuning to the DARWIN catalog.
  • Prisma (Prototype Research Instruments and Space Mission technology Advancement), a Swedish project with joint European funding, will be launched in the fall of 2008, with the objective of studying guidance, navigation, control and sensor techniques as the two spacecraft involved demonstrate formation flying, so necessary to the accuracy of the DARWIN attempt.
  • PROBA3, not yet fully funded, but intended as a follow-up to PRISMA and an attempt to further advance formation flying techniques.
  • Pegase/PERSEE, designed to study extrasolar giant planets at near-infrared wavelengths, a mission that could be extended to brown dwarfs and other targets of astrophysical interest. Not yet funded, this mission may well wind up merged with PROBA3.

How close are we to making DARWIN a reality? Here’s the report’s conclusion, referring to the TRL (Technology Readiness Level) scale from 1 to 9, in which a 6 indicates readiness for a technology demonstration and a 9 is readiness for launch and operations:

The message from the last decade of Darwin technology development is clear: if the Research and Technology effort that has been pursued in both Europe and the United States continues vigorously, Darwin’s technology will reach TRL 5/6 by 2010, allowing it to be selected as ESA’s first L mission for launch in 2018-2020.

So that’s the time frame. With as much play in the numbers as this suggests, and given the amount of work needed in tuning up both interferometry and formation flying, this may be an optimistic target. ESA is upfront about viewing DARWIN as one of the most ambitious missions it has ever undertaken. The potential scientific reward, however, is huge. With spectroscopy of individual Earth-like planets, we’ll have a good chance at discovering whether or not we’re looking at living worlds. No possibility could be more tantalizing.

The DARWIN mission proposal to ESA can be downloaded here in basic form, with a high-resolution version also available.


Robin Goodfellow July 26, 2007 at 16:59

Other missions to keep an eye on:
The Space Interferometry Mission (SIM), which will test many of the key technologies and techniques of space borne optical interferometry.

Terrestrial Planet Finder (TPF). Darwin is a close relative to the TPF-interferometer design.

philw July 26, 2007 at 17:21

The problem with Darwin, SIM and TPF is that every year they are the same or even more years further away. And the minor detail that they are not hardware funded.

enzo July 26, 2007 at 20:19

I agree with philw above : Darwin was supposed to launch around 2012-13,
now is pushed to 2020.

And another thing : can anyone make a comparison of what some gigantic
mission like Darwin, including all this yet-to-prove technology can do better
than simpler occulter missions like the one proposed by Cash or Umbras
( ?
How much better is it, considering all it needs to be developed for it to work ?


ljk July 27, 2007 at 11:02

Spectropolarimetric signatures of Earth-like extrasolar planets

Authors: D. M. Stam

(Submitted on 26 Jul 2007)

Abstract: We present results of numerical simulations of the flux (irradiance), F, and the degree of polarization (i.e. the ratio of polarized to total flux), P, of light that is reflected by Earth-like extrasolar planets orbiting solar-type stars, as functions of the wavelength (from 0.3 to 1.0 micron, with 0.001 micron spectral resolution) and as functions of the planetary phase angle. We use different surface coverages for our model planets, including vegetation and a Fresnel reflecting ocean, and clear and cloudy atmospheres. Our adding-doubling radiative transfer algorithm, which fully includes multiple scattering and polarization, handles horizontally homogeneous planets only; we simulate fluxes and polarization of horizontally inhomogeneous planets by weighting results for homogeneous planets. Like the flux, F, the degree of polarization, P, of the reflected starlight is shown to depend strongly on the phase angle, on the composition and structure of the planetary atmosphere, on the reflective properties of the underlying surface, and on the wavelength, in particular in wavelength regions with gaseous absorption bands. The sensitivity of P to a planet’s physical properties appears to be different than that of F. Combining flux with polarization observations thus makes for a strong tool for characterizing extrasolar planets. The calculated total and polarized fluxes will be made available through the CDS.

Comments: 31 pages text, 17 figures, 1 table Submitted to A&A

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0707.3905v1 [astro-ph]

Submission history

From: Daphne Stam [view email]

[v1] Thu, 26 Jul 2007 12:07:44 GMT (325kb)

philw July 28, 2007 at 11:08

Enzo, I agree about your simpler, more achievable approach. I do not understand the sci-politics of mission lobbying well enough to unserstand why such lower cost, less risky yet scientifically rewarding missions aren’t part of NASA’s ‘plan’. Me, I’m frustrated waiting for Kepler, now slipped to 2008 launch.

enzo July 28, 2007 at 19:28

Regarding Kepler, there is COROT, currently operating and apparently producing better than expected data. It is now expected to detect Earth size planets.

philw July 29, 2007 at 15:31

You go, COROT! A slight gripe: ESA tends to embargo most data for about 1 year for the principal researchers so they can publish their research first without being precipitously scooped by non-participants. Bummah!

enzo July 29, 2007 at 17:48

Yes, they do, but I suspect that if they really find an Earth size planet they will announce that. In fact they have already announced the first COROT planet.
Anything special (like the first, the smallest, the ..est) will probably be announced, full data will come later.


andy July 29, 2007 at 18:35

Yeah, actual data on the first COROT planet is still to be released.

Fortunately the embargo means they can take the time to do a proper analysis of the habitability of any planet, rather than screaming “habitable” and then going “er, we forgot about the greenhouse effect” later.

ljk January 31, 2008 at 12:17

Towards a Small Prototype Planet Finding Interferometer: The next step in planet finding and characterization in the infrared

Authors: W.C. Danchi, D. Deming, K. G. Carpenter, R. K. Barry, P. Hinz, K. J. Johnston, P. Lawson, O. Lay, J. D. Monnier, L. J. Richardson, S. Rinehart, W. Traub

(Submitted on 30 Jan 2008)

Abstract: During the last few years, considerable effort has been directed towards large-scale (more than $1 Billion US) missions to detect and characterize earth-like planets around nearby stars, such as the Terrestrial Planet Finder Interferometer (TPF-I) and Darwin missions.

However, technological and budgetary issues as well as shifting science priorities will likely prevent these missions from entering Phase A until the next decade. The secondary eclipse technique using the Spitzer Space Telescope has been used to directly measure the temperature and emission spectrum of extrasolar planets. However, only a small fraction of known extrasolar planets are in transiting orbits.

Thus, a simplified nulling interferometer, which produces an artificial eclipse or occultation, and operates in the near- to mid-infrared (e.g. ~ 3 to 8 or 10 microns), can characterize the atmospheres of this much larger sample of the known but non-transiting exoplanets. Many other scientific problems can be addressed with a system like this, including imaging debris disks, active galactic nuclei, and low mass companions around nearby stars.

We discuss the rationale for a probe-scale mission in the $600-800 Million range, which we name here as the Small Prototype Planet Finding Interferometer (SPPFI).

Comments: 8 pages, 4 figures, white paper for Exoplanet Task Force, March 2007

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0801.4752v1 [astro-ph]

Submission history

From: William Danchi [view email]

[v1] Wed, 30 Jan 2008 20:04:56 GMT (1420kb)

ljk February 25, 2008 at 11:18

The achromatic chessboard, a new concept of phase shifter for Nulling Interferometry – I. theory

Authors: Daniel Rouan, Didier Pelat

(Submitted on 22 Feb 2008)

Abstract: Direct detection of a planet around a star in the mid-IR, requires a nulling interferometer featuring an achromatic phase shift of pi on broad range. A new concept for designing such an achromatic phase shifter is presented here. The major interest of this solution is that it allows a simple design, with essentially one device per beam.

The heart of the system consists in two cellular mirrors where each cell has a thickness introducing for the central wavelength, a phase shift of (2k+1)pi or of 2k pi on the fraction of the wave it reflects. Each mirror is put in one of the collimated beams of the interferometer. Because of the odd/even distribution, when recombining the two beams, a destructive interference is produced on axis for the central wavelength . If the distribution of cells thickness follows a rather simple law, based on the Pascal’s triangle, then the nulling is also efficient for a wavelength not too far from the central wavelength. For instance, with two mirrors of 64×64 cells, one reaches a nulling of 1.e-6 on more than one complete octave.

This could satisfy the specifications of space mission as Darwin. We also show the way to distribute the cells in the plane of the pupil for the optimum isolation of the planet image from the residual. We present the nulling performances of those various configurations.

Comments: Accepted in Astronomy and Astrophysics

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0802.3334v1 [astro-ph]

Submission history

From: Daniel Rouan [view email]

[v1] Fri, 22 Feb 2008 14:56:41 GMT (365kb)

ljk May 14, 2008 at 13:37

DARWIN – A Mission to Detect, and Search for Life on, Extrasolar Planets

Authors: C. S. Cockell, A. Leger, M. Fridlund, T. Herbst, L. Kaltenegger, O. Absil, C. Beichman, W. Benz, M. Blanc, A. Brack, A. Chelli, L. Colangeli, H. Cottin, V. Coude du Foresto, W. Danchi, D. Defrere, J.-W. den Herder, C. Eiroa, J. Greaves, T. Henning, K. Johnston, H. Jones, L. Labadie, H. Lammer, R. Launhardt, P. Lawson, O. P. Lay, J.-M. LeDuigou, R. Liseau, F. Malbet, S. R. Martin, D. Mawet, D. Mourard, C. Moutou, L. Mugnier, F. Paresce, A. Quirrenbach, Y. Rabbia, J. A. Raven, H. J. A. Rottgering, D. Rouan, N. Santos, F. Selsis, E. Serabyn, H. Shibai, M. Tamura, E. Thiebaut, F. Westall, White, J. Glenn

(Submitted on 13 May 2008)

Abstract: The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The detection of planets with a wide range of masses demonstrates that extra-solar planets of low mass exist. In this paper we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines including astrophysics, planetary sciences, chemistry and microbiology.

Darwin is designed to detect and perform spectroscopic analysis of rocky planets similar to the Earth at mid-infrared wavelengths (6 – 20 micron), where an advantageous contrast ratio between star and planet occurs. The baseline mission lasts 5 years and consists of approximately 200 individual target stars. Among these, 25 to 50 planetary systems can be studied spectroscopically, searching for gases such as CO2, H2O, CH4 and O3.

Many of the key technologies required for the construction of Darwin have already been demonstrated and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.1873v1 [astro-ph]

Submission history

From: Glenn White Prof [view email]

[v1] Tue, 13 May 2008 15:37:51 GMT (2326kb)

ljk October 31, 2008 at 0:09

Target star catalog for Darwin: Nearby Stellar sample for a search for terrestrial planets

Authors: L.Kaltenegger, C.Eiroa, C. V. M. Fridlund

(Submitted on 28 Oct 2008)

Abstract: In order to evaluate and develop mission concepts for a search for Terrestrial Exoplanets, we have prepared a list of potential target systems. In this paper we present and discuss the criteria for selecting potential target stars suitable for the search for Earth like planets, with a special emphasis on the aspects of the habitable zone for these stellar systems. Planets found within these zones would be potentially able to host complex life forms.

We derive a final target star sample of potential target stars, the Darwin All Sky Star Catalog (DASSC). The DASSC contains a sample of 2303 identified objects of which 284 are F, 464 G, 883 K, 615 M type stars and 57 stars without B-V index. Of these objects 949 objects are flagged in the DASSC as multiple systems, resulting in 1229 single main sequence stars of which 107 are F, 235 are G, 536 are K, and 351 are M type.

We derive configuration dependent subcatalogs from the DASSC for two technical designs, the initial baseline design and the advanced Emma design as well as a catalog using an inner working angle cut off. We discuss the selection criteria, derived parameters and completeness of sample for different classes of stars.

Comments: 14 pages, 8 figures, 4 tables (available at this http URL or email A&SS accepted

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0810.5138v1 [astro-ph]

Submission history

From: Lisa Kaltenegger [view email]

[v1] Tue, 28 Oct 2008 20:51:01 GMT (1285kb)

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