TPF-I SWG Report - Exoplanet Exploration Program - NASA

TPF-I F L I G H T B ASELINE D ESIGN
30
25
All (1014)
2 Earth mass (231)
1 Earth mass (100)
0.5 Earth mass (44)
0.25 Earth mass (22)
0.1 Earth mass (9)
Distance / pc
20
15
10
5
0
0 50 100 150 200
Projected radius of Inner Habitable Zone / mas
Figure 5-21. Planet mass sensitivity for a single array rotation of 50,000 s. 9 nearby stars can be
surveyed for planets in the Habitable Zone with masses as low as 0.1 Earth mass. The mass
sensitivity improves as T 0.75 , assuming constant density of the planet.
A candidate selection will be followed up with further observations to determine the orbit and to rule out
the possibilities of background sources and lumps in the exozodiacal emission. This phase of the planetfinding
process is less well studied than the initial detection, but it should be greatly eased by the
excellent angular resolution of the stretched X-array (see Section 5.8). The spectroscopic characterization
phase is the subject of the next section.
5.8.3 Spectroscopy
Following detection and orbit determination, the goal is to obtain a spectrum of candidate planets. The
outputs of the single-mode spatial filters are dispersed into ~100 spectral channels on a detector array.
The array always observes at the full spectral resolution because the response on the sky is wavelengthdependent,
and lower spectral resolution will restrict the useful field of view. The channels are co-added
in the post-processing to maximize the SNR for detection and orbit determination, but this data also
provides a first look at the spectrum, albeit with low SNR.
121