According to NASA nearly 2000 exoplanets had been discovered by 2016, and the search continues - AQA - A-Level Physics - Question 5 - 2017 - Paper 4

Detecting an Earth-like planet presents numerous challenges. Here are three methods commonly employed, along with their associated difficulties:

1. Transit Method

The transit method detects exoplanets by measuring dips in brightness as planets cross in front of their host stars. The difficulty here lies in the precision required; the fluctuations in light can be minimal, and distinguishing these from noise in the data is challenging. Additionally, this method is more effective for larger planets, making it less likely to detect smaller Earth-like planets.

2. Radial Velocity Method

This technique measures the star's wobble due to the gravitational pull of an orbiting planet. The main challenge is identifying the minute shifts in the star's spectrum caused by this motion, which requires extremely sensitive spectrometers. This method also poses difficulties in cases where multiple planets are located in the same system, complicating the interpretation of data. This method tends to favor larger, more massive planets over smaller ones, which can lead to bias in detected samples.

3. Direct Imaging

Directly capturing images of exoplanets can be done using advanced techniques like coronagraphy. The challenges include the significant contrast between the host star and the planet, which makes imaging extremely difficult. High-resolution telescopes and adaptive optics are required to filter out star light, yet even with this technology, the ability to directly observe Earth-like planets remains limited.

Conclusion and Success Suggestion

Given the challenges presented by these methods, a combination approach may yield the most successful outcomes. For instance, using transit observations to identify potential candidates followed by radial velocity measurements could synergistically enhance detection rates. Moreover, advancements in technology and techniques for direct imaging may soon enable us to observe Earth-like planets more effectively in the near future.