Using the Sun to estimate Earth-like planets detection capabilities.I. Impact of cold spots

TL;DR

This study investigates how stellar spots, similar to sunspots, affect the ability to detect Earth-like planets in the habitable zone using radial velocity measurements, emphasizing the importance of sampling frequency over measurement precision.

Contribution

It demonstrates the impact of sunspot-like activity on RV detection of Earth-mass planets and highlights the need for intensive, well-sampled observations during low stellar activity periods.

Findings

Detection requires weekly or better sampling over several years.

Temporal sampling is more critical than measurement precision.

Cooler spots and plages could further hinder planet detection.

Abstract

Stellar spots may in some cases produce radial velocity (RV) signatures similar to those of exoplanets. To further investigate the impact of spots, we aim at studying the detectability of Earth mass planets in the habitable zone (HZ) of solar type stars, if covered by spots similar to the sunspots. We have used the Sunspots properties recorded over one solar cycle between 1993 and 2003 to build the RV curve that a solar type star seen edge-on would show, if covered by such spots with Tsun -Tspot = 550K. We also simulate the RV of such a spotted star surrounded by an Earth mass planet located in the HZ. Under present assumptions, the detection of a 1 M Earth planet located between 0.8 and 1.2 AU requires an intensive monitoring (weekly or better), during several years of low activity phasis. The temporal sampling is more crucial than the precision of the data (assuming precisions in the range [1-10] cm/s). Cooler spots may become a problem for such detections. Also, we anticipate that plages, not considered in this paper, could further complicate or even compromise the detections.