Copernicus
55 Cancri A · HD 75732 · HIP 43587 · 12.55 pc · 5 confirmed planets
Section 01
General Information
Janssen (55 Cnc e) was observed by JWST in 2024, revealing a possible CO₂-rich atmosphere — the first direct atmospheric detection of a rocky super-Earth. The C/O ratio of 55 Cnc A remains contested (Teske et al. 2013: C/O = 0.78 ± 0.08). The Codex is measuring it independently with HARPS R~115,000.
Stellar Parameters
| Parameter | Symbol | Value | Source |
|---|---|---|---|
| Effective temperature | Teff | 5196 K | von Braun et al. 2011 — CHARA interferometry |
| Surface gravity | log g | 4.41 | von Braun et al. 2011 |
| Metallicity | [Fe/H] | +0.32 dex | Fischer & Valenti 2005 |
| Microturbulence | ξ | ~0.9 km/s | Spectroscopic self-consistency |
| Spectral type | — | K0 IV-V | Literature |
| Distance | d | 12.55 pc (40.9 ly) | Gaia DR3 |
Known Planets
| Planet | Mass | Type | Semi-major axis | Hab zone |
|---|---|---|---|---|
| Janssen (e) | 8.08 M⊕ | Super-Earth | 0.0154 AU | No — lava world |
| Galileo (b) | 264 M⊕ | Hot Jupiter | 0.1134 AU | No |
| Brahe (c) | 54.4 M⊕ | Saturn-mass | 0.2373 AU | No |
| Harriot (f) | 45.4 M⊕ | Neptune-mass | 0.7708 AU | Marginal |
| Lipperhey (d) | 1074 M⊕ | Jupiter-mass | 5.74 AU | No |
Section 02
NASA Interactive Visualization
Section 04
Our Findings
Section 05
References & Credits
Key Literature
von Braun et al. (2011), ApJ 740, 49 — stellar parameters
Fischer & Valenti (2005), ApJ 622, 1102 — [Fe/H] = +0.33
Teske et al. (2013), ApJ 778, 132 — C/O = 0.78 ± 0.08
JWST GO-1952 — Janssen thermal emission
Data Sources
NASA/IPAC Exoplanet Archive
SIMBAD / CDS — stellar parameters
Hipparcos / Gaia — parallax & distance
Image Credits
Credit: NASA/ESA/CSA — Artist concept of Janssen (55 Cnc e)
Interactive sky: CDS Aladin Lite v3 / DSS2
NASA Eyes: NASA/JPL-Caltech
Pipeline
HARPS S1D — ESO Science Archive
Analysis: The Exoplanet Codex