Question: Can you summarise the technical design of the PlaVi payload in a few sentences?
PlaVi consists of a single 2-mirror afocal telescope with an aperture of 32 cm and a FOV of 9 square
degrees. It has 3 detectors: two that cover the entire visual wavelength range, and one passively cooled
detector for the near-IR from 900 to 1700 nm. The instrument is capable of measuring high-precision time
series with a cadence as short as 10 s. All the science requirement are driven by the main science goals.
Q: Why do you propose photometry in several band-passes rather than a single ‘white’ bandpass,
Unlike Kepler, our main goal is to characterize known exoplanet systems in exquisite details that
go way beyond finding new exoplanets. Such characterisation is the next logical step after discovery,
and PlaVi would be the first space mission dedicated to this. For its central mission objectives, photometry
in several band-passes gives much richer and necessary information than a single band-pass. This
information is derived from the comparison of signal strengths at the different wavelengths. One of the
band-passes will be in the near infrared, because planet signals are stronger there than in the optical.
Nevertheless, PlaVi also has discovery capabilities thanks to its flexibility.
Q: Does PlaVi have supplementary science goals as well?
Yes, it does. Although our focus is on exoplanetary systems, supplementary science goals are important
to PlaVi. For the planet hunting missions CoRoT and Kepler, the scientific output in terms of publications
and citations turns out to be almost as large from the non-planetary science as from the planetary
science. That is, supplementary science is very important for the huge success of these missions. In
case of PlaVi, supplementary science comes naturally with the relatively large FOV, together with the
long runs (both requirements driven by exoplanetary science). This opens up the opportunity for eclipsing
binary star research, asteroseismology, stellar activity studies, observations of stellar clusters, the
pursuing of particular targets of opportunity, etc. This is a very important bonus that comes for a very low
Q: Why did you choose for an Earth-trailing orbit (ETO) and not a low-Earth orbit (LEO)?
From the experience with Kepler, and Spitzer, we know that an ETO has significantly better observing
conditions to gather time series than a LEO. This is due to the near perfect stability of the ETO’s
environment, due to the ETO’s much better pointing flexibility and due to the observation without
interruptions. Kepler has shown that long-term stability is the right choice for our objectives.. Only with an
ETO is it possible to perform day-to-months long pointings of ANY part of the sky. For example, a Solar
Synchronous orbit allows only the observation of 30-40% of the entire sky without interruptions, and never
with pointings lasting more then 5-8 weeks (depending on the altitude of the SSO), significantly lowering
the cost effectiveness of the mission, and deteriorating the quality of the science data.
Q: What are the benefits of having a 9 square degrees FOV?
Our planetary science objectives require high-precision multicolour photometric observations taken with
an excellent duty cycle. We specified the largest possible FOV that permits the fulfilling of these scientific
requirements. This FOV maximises the scientific return of the mission by enabling multiple targets per
exposure. Planetary systems that are nearby in the sky (e.g. in a cluster) may be observed and a myriad
of supplementary science targets and objectives are possible.
Q: Doesn't your telescope design look a bit like the one of CoRoT?
Yes, it does, and we consider it an asset of our design. In our opinion, re-using some of the existing
knowledge and expertise is one of the key features of an S-mission design. The CoRoT telescope is a
well-proven and successful design, for which the manufacturing and operational aspects are thoroughly
understood. That said, we did not simply duplicate the CoRoT mission: we have different science goals,
different targets, different detectors, and a different orbit.
Q: Doesn't your platform look like the one of the Ingenio satellite?
Yes, indeed, and just like for our telescope we consider this an asset too. Our initial studies show that we
can re-use ~70% of the Ingenio platform. This makes it excellently suited for a low-budget S-mission like
Q: How does PlaVi compare with the Exoplanet Characterisation Observatory (EChO)?
These missions are complementary to each other. PlaVi is an S-mission that focuses on multi-band
photometry, while EChO is an M-mission focusing on IR-spectroscopy. The two missions would be an
ideal tandem, putting Europe firmly at the front of planetary science. The time-line of PlaVi would permit an
in-depth characterisation of EChO targets prior to EChO’s launch, thereby strongly improving the
efficiency of that mission. We are in contact with the EChO consortia discussing and collaborating on the
Q: How does PlaVi compare with Plato?
The philosophy behind PlaVi is different from Plato, which is another ESA M-mission proposal. Plato will
observe very large numbers of stars in a very large FOV for a very long time, aiming thereby to discover
a large number of new exoplanets around relatively bright targets. PlaVi focuses on the next step, the
characterisation of the most interesting exoplanet systems that will be known, using multicolour
photometry. PlaVi's target list will be extended with suitable targets, detected by next-generation
ground-based exoplanet surveys such as MASCARA and NGTS, which will be available by the time PlaVi
will be launched.